What are the most important things to bring on a ride?

For me, I really regret not having a multi tool with me. If I had it, I could have removed the broken derailleur and cut the chain to fit into a free wheel. At least, it would be enough until I reach a mechanic.

A mobile phone. These days, irrespective of where you're riding, what you're riding and over what terrain or distance, there's no excuse for being deliberately out of contact. We can't guarantee being in an area of reception, but if you haven't got a phone you'll never know.

Additionally, a huge benefit of smart phones are the apps that can do more than just call for assistance. e.g. I have an app which lists all bike shops in London, with maps, reviews and opening hours. A couple of times I've been stuck in the middle of somewhere unfamiliar and in need (after the second puncture of the day without a second spare tube): fire up the app, where's the nearest open shop and then it can lead you there.

Water makes a big effect on how long you can last whilst touring. If you can, get a water bladder that can fit inside your backpack, you can drink whilst you cycle without having to get of the bike and lose your momentum. Sport and energy drinks don't give quite as much hydration as water alone.

On the road:

Lights even if you plan to be back in daylight. If you do have a mechanical problem and have to make repairs before you can keep going you may be riding later than you had planned and in fading light.

On all rides:

Puncture repair kit and/or spare inner tube

For a commuter:

A good weather proof bag/trunk is essential when commuting from place to place. Weather you have to make a quick stop at the store after work or need a place to carry your gear no matter what mother nature has to offer a solid bag will make commuting so much easier.

This is the one I use:

I like this one because like most Topeak products it clips on to my rack so I don't have to worry about it being secure, it has plenty or storage space, and I notice that it is slightly insulated so it will keep things like groceries cool.

The number-one situation cyclists will face on a ride (aside from experiencing the awesomeness that is riding) is a flat tire. To fix that, you'll want either a spare tube or a patch kit -- or both. Of course, these are useless without something to pump them up! A frame pump or a C02 inflator will take care of that. Make sure to bring a cartridge for the C02 inflator. (They make devices that are both, but my experience is that they tend to do both jobs terribly.) Also, make certain you know how to change a flat. If pressure is important to you, get one with a pressure gauge.

Tools: Unless you're on a loaded touring bike, you'll want to keep your saddle bag light and bring along a multitool, as opposed to full-sized tools. I won't recommend any one tool, but something that includes the three sizes of allen keys and a chain tool will handle nearly any situation you're going to repair by the side of the road: Broken spokes, a split chain, a loose rack, adjusting a slipped seat-post, a rattling fender.

Duct tape or electrical tape: Wrap a small amount of it around a short pencil and toss it in your bag. You can use this to fix grip tape, repair a rip in a bag, or hold a headlight together. You can also toss a zip tie in there while you're at it.

Spare batteries are helpful if you have lights or a cycling computer.

I always bring along a cell phone.

A first aid kit is always a good idea. You can pare it down to the essentials, especially if you're on a supported ride, but it's a good idea to be able to take care of yourself until the sag wagon arrives. If you have a medic alert tag or a card, bring that as well. (I keep a tag on my body as well as one on the outside of my trunk rack bag.)

Water: I can't stress this one enough. Bring as much of it as you can carry comfortably, and always fill up when you have the opportunity. Dehydration is no fun!

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This is a pretty minimalist kit. If you want advice on a kit for touring, there's a thread here on the site about just that.

My bike is my main mode of transportation. As such, I installed a carry-all on the back. I keep a multi-tool, two spare tubes, spare batteries for the bike lights, a small hand-pump, and a basic wrench. This still leaves plenty of room in the carry-all for rain-gear, a light load of groceries, or whatever else I need to lug around.

I always keep some money in my bag. It's useful to have some on you in case, for example, you forget to take some for parking or need extra food and there's a shop nearby. I've done both of these.

Utmost? In order of probability....

1. The ability to fix a flat out in the middle of nowhere. Which means an extra tube, patch kit, CO2 or pump, tire levers, etc.

2. A cycling tool set or multi-tool allowing you to adjust any of the major components of your bike.

3. Odds and ends, like, duct tape, a bit of stiff wire, replacement nuts/bolts, chain-link, zip-tie, etc.

4. Small, efficient clip-on lights.

This is pretty much what my seat bag contains. Other than that, water, the mobile phone, and my wallet and keys. These items go along everywhere anyway. So, don't consider them to be cycling essentials.

Given the choice, I will take the ability to self-sufficiently repair a flat over the mobile phone. Odds are, I'll need to fix a flat far more often than the day when I need major help. So flat fixing ability is the "utmost'.

Lessee -- roughly in priority order --

• Water. Even on a short 30-minute ride I always carry water. Not that I drink that much on a short ride, but should I fall and get "road rash" a squirt of water can quiet the burn and make it possible to complete the ride in relative comfort.
• Spare tube, tire "irons" (I prefer a "Slick Stick"), and a decent frame pump. (Many frame pumps are worthless -- be sure to actually try using yours to completely inflate a tire before you have to depend on it.) A patch kit is a good idea as well.
• Money -- in addition to a wallet you may be carrying, stash $20 or so in a "secret" place in your tool bag or whatever.
• Multi-tool -- screwdriver, a few allen wrenches, a few hex wrenches. Not only used to tighten things, but the screwdriver may be needed to pry a chain out from behind the granny ring, pry the wax out of your ears, etc.
• Cell phone.
• Hockey tape. I carry this rather than duct tape or electrical tape because it's so versatile. It can be used to wrap a handlebar, secure a loose fender, hold in place an impromptu bandage, and a dozen other things. (My handlebars are permanently wrapped with hockey tape, which I refresh about every two years. Much better grip than standard handlebar tape.)
• Zip ties, in a couple of small/medium sizes. Can be used to secure a bag if the clips/straps break, hold on a fender if the screw falls out, etc.
• Small first aid kit. You don't really need (or want the weight/bulk of) a packaged kit. A plastic bag containing a half-dozen band-aids, about 4 gauze pads, some antiseptic cream, and a small roll of adhesive tape is all you need.
• Spoke wrench (if the one on your multi-tool isn't very good). Most often used on a wheel with a broken spoke to loosen the opposite side so that the brakes don't rub (quite so badly).
• A short length of chain, some "repair links", and a chain tool. I no longer use a chain tool often enough to be good at using it, so the repair links (SRAM) are the way to go. But you still need the tool to "crack" a damaged chain and remove damaged links, and to similarly "crack" the length of repair chain. (NB: You need to be sure that the chain, repair links, and tool are the right size for your chain. There are 3-4 different common chain widths these days.)

Water. Multi-Tool. Knife. Spare tube. Pump (I think CO2 cartridges are wasteful and non-evironmentally-friendly) Cell phone. My key is to keep my bike well-maintaned so I don't have to concern myself with the possibility that my chain will snap or my derraileur will explode 100 miles from nowhere.

I carry a lot of stuff with me on my road bike. Enough tools to nearly completely strip and rebuild the bike plus spare tubes, usually 1 tire, CO2 inflator, AND a hand pump. Repairs are plan A. My plan B involves the cell phone I also carry. I consider it more important than all the tools. Plan C is the pair of comfortable walking shoes that are also stuffed into my backpack. Since that's my last chance, I consider it the MOST important. Yes, I've been all the way down to plan C once in my riding... Luckily it was only a couple miles I had to walk, but even that short distance would have been horrible in the cycling shoes!

(Reusing an answer to What should I carry on day trips for emergencies? as I always bring the same toolkit not depending on the length of the ride.)

Here's my toolkit. A mini pump is carried separately external to the toolkit because the mini pump does not fit into the limited size toolkit. When I ride a fatbike, I carry its fat spare tube in a bottle holder, not using the spare inner tube in my toolkit.

The toolkit is 20 cm x 10 cm x 4 cm leather container originally intended for a lux (light) meter. I reused it for my bicycle emergency toolkit, realizing it has a very useful size and is durable. The leather container has a zipper closure mechanism.

Total weight: 685 g

• leather container only: 63 g
• spare inner tube (Continental Tour 28 All, 32-47 / 622): 167 g
• Allen keys 2.5, 3, 4, 5, 6, 8: 120 g total
  • 8 mm: 56 g
  • 6 mm: 29 g
  • 5 mm: 18 g
  • 4 mm: 10 g
  • 3 mm: 5 g
  • 2.5 mm: 3 g
• Stein mini cassette lockring tool bag with extra spacers and longer pin: 60 g
  • The extra spacers and longer pin allow using it for brake disc lockring too
• mini combined chaintool / spoke wrench: 55 g
• 4 inch adjustable wrench: 52 g
  • I use this as leverage to cut the end of a Shimano reinforced chain pin, and in those rare cases I need something to turn six-sided nuts. Can also be used to true disc brake rotors.
• tire levers (two of them, blue levers from Park Tool): 26 g
• Torx keys T25, T30: 26 g
  • T30 Torx key: 17 g
  • T25 Torx key: 9 g
• tube patches, glue and sandpaper in plastic package: 18 g
• wrench-type Phillips / slotted screwdriver: 18 g
• wheel security skewer wrench (similar to Allen but 5-sided): 16 g
  • I use security skewers instead of quick release skewers to make wheel theft less likely
• plastic zip ties: 10 g
• three Park Tool TB-2 tire boots: 8 g
• five Shimano 8-speed reinforced pins in ziploc bag labeled with speed count: 7 g
• disposable cloth, anti-microbial wipe and adhesive bandage: 6 g
• small KMC chain lube tube: 5 g
• three 10-speed Shimano reinforced pins in ziploc bag labeled with speed count: 5 g
• two 11-speed KMC Missing Link quick-links: 5 g
  • My fatbike came with a quick link chain. I'm planning to replace it with a reinforced connecting pin chain when it wears out. Usually I don't use quick links.
• US Shelby Co P-38 can opener: 5 g
• DIY rim tape tire boot (narrow and long): 4 g
• three 2mm spoke nipples: 3 g
• rubber band: 2 g
• two spare long spoke reflectors: 2 g
• DIY duct tape tire boot: 2 g
• razor blade: less than 1 g (the scale said 0 g)
  • I use this for removing tube seams before patching

The mini pump I use is Quickex Quicker Pro, no longer sold (unfortunately, as it as a double action two-chamber pump allowed very quick inflation for its size). It weighs 181 g.

When riding, I also always have a mobile phone with me. The mobile phone case has a credit card pocket where I always keep a credit card.

The total weight with mobile phone, pump and toolkit is about 1 kilogram. I carry them in a shoulder bag.