keeping track of what a branch is for

Ok - here's another one...

I've started to create a lot of branches (like one per feature I'm
working on), but I'm starting to have trouble keeping track of what
each branch is for. Also, I'd like to keep track of a todo list for
each branch.

Is there a good way to keep track of these details with git? Using a
repository file kinda works except when merging back into the master
branch.