LOL, I've always used a coin or a flathead to pop the master link if needed. Needle-nose come in handy tho.
For my bikes I carry my trusty Leatherman Surge + bit set, a 10MM wrench (engine), a 15MM wrench (axles), kit plug tool, and a new plug. At the very least, I recommend keeping a tool that's the same size as your brake pad bolts if you have rim-grabbing brakes. Often that's just a single allen wrench.
It's always good to give your bike a once-over before any ride, making sure nothing has worked loose. Things like nuts and bolts and brake pads get loose even on a pedal bike over time, they have a real knack for moving around on a motorized bike!