Being a bit of a simple person I like to keep my bag simple, with focus on only whats most useful and lightest. and that is the fold up hex wrench set.
It is the only tool I carry with me everywhere when I ride the bike. It’s a go-to for the seat height and angle, and for the handlebar height and angle. Most of the time if your bike isn’t dialed in to your size and height this will be a necessity to take with you and play around with to adjust the bike to your riding comfort.
All the other stuff usually can be left at home unless your going on a long ride, lets say across the country on a bicycle tour.