This in combination with a `git diff` in a split shell works very well for me. For adding changes, I often use `git add -p` - this also gives a nice opportunity to think about a change again. As a bonus, if I did not yet push, I can extend the commit (using --amend) or roll back to it when doing experimental changes. There is also the option to `git stash` some work away.

Hell, you could write it down in a separate text file if it’s really that big of a painpoint.

At that point I think the case for a tool like git-plan is pretty strong.

I think most teams use a bug tracker for this sort of thing, tbh.