How do you put a list inside of an object C#?

New to C#, sorry if the wording is a little off. I want to make one of my fields in an object as a list. My below code does not let me access the list.

class Bag
{
    public string name;
    public int space;
    public int cost;
    List<string> items = new List<string>();


    public Bag(string name, int space, int cost, List<string> items)
    {
        this.name = name;
        this.space = space;
        this.cost = cost;
        this.items = items;
    }

I am not able to use items when using the below code:

bag1.items.Add("Money");