Whatever you do, do not let yourself become too idle. It will make the days drag on, and at the end of the day it will feel like you wasted the day.

You should at least use version control for what you are working on. Even if it is just a local Git repo (that you keep backed up, of course). Same with ticketing, either pick up one of the open source ticketing systems just for your own sanity, or take time to create your own ticketing system if there is that much slack time.