I don't get a chance to work on my side project every day. So I've noticed an annoying 'reload' time when I come back to it after a few days, that it takes to figure out where I was and how to get started again. To help, I've found myself keeping a simple log in a text file with notes to myself. It's not great, and I'm sure there's a better way. (By log I mean something different than commit messages. It's more like a personal journal, with notes on what I did, where I left off and what I have to do next.)
Does you do something to optimize how quickly you get back into a project that you only get to work on occasionally? E.g. I have a friend who chats with Slackbot in a private room, though I'm not sure it's much better than a text file.