As far as docking goes, a lot of that just comes with practice and patience. Go slow until you are more comfortable. If you have never launched/retrieved before, go on a slower weekday to practice and figure out a process that works for you.
As far as stuff to have on board, start with all the required safety gear and go from there. I have a small water proof ammo box that I keep a small set of tools in (Phillips and regular screw drivers, some adjustable wrenches, pliers, and a socket set with the sockets that I might need), an extra plug, electrical tape, an extra flair, cheap rain gear, spark plugs, and a small voltage meter. I also keep my insurance and registration card in there. I have a set of jumper cables in the boat. That I actually used late last year when my main battery went bad on me and I had to jump across one of my trolling batteries to start the motor to get back in to harbor. I have an extra fuel line and rope too....I probably have too much stuff
Im sure I am forgetting something, but I'm sure some others will chime in with what they have onboard.