Pump and patch kit and knowing how to use them.
I carry a lock.Since I can't afford to replace my good bike I carry a good U-bolt lock. I even lock up on club rides when we stop for pie and brownies and my bike is surrounded by more valuable bikes. At least carry a little cable lock. I like using gloves. Eye protection is a good idea on or off road. Some way to carry this stuff. Wallet, cell phone. I carry a set of grape pruning shears I found on one ride and often clear brush blocking the path or bike lane. Bloody powerful set of lights when I might have to ride at night.