ExeFunk Tip:
If you've got a MacBook, opt-v makes a nice checkmark character √ for making quick casual lists.
My system:
+ To Do - this item is undone
+ This is a subtask that is undone
√ This item is done
? I don't know if this should be done
x I decided against doing this
- I'm making a note or something that doesn't need to be done.
If I need to get real fancy, I copy/paste in a 1/2 symbol for things that are partly done. (There is no shortcut key on Mac but I could make an auto-replace shortcut if I wanted.)
I've got a number of other list systems, but this is what I use for writing projects (lists go in the related Scrivener file) and when I'm making quick lists in notes apps.