To use git effectively (and as intended) I make small atomic commits, while I do have longer sessions where I do change not only one thing. Thus, I make heavy use of git a
Maybe you could try writing some pre-commit hook that alerts you if you have untracked files. This will require you to always keep your git directory clean to work, though (and obviously you'll need to keep a up-to-date .gitignore).
Also try git add -i
which is similar to git add -p
but also has an interface for adding new files.