As with anytime you leave your home it’s always good practice to have identification, a cell phone, and cash.
Your standard equipment should include a good lock—you’ll need it if you are going to leave your bike unattended for even a very short amount of time. For the best security, use a cable lock to loop through your seat and a U-lock to link the bike frame and front wheel to the bike rack. A heavy chain lock can do all three, but keep in mind they can be heavy to carry.
You can also bring an extra wheel tube, airpump, and levers for fixing your bike on the go if need be.
Only bring the tools for the work you know how to do.