Get someone to do a load test on your battrey, just to make sure it will be up to the task when needed. Check all wiring for corosion at terminal blocks and back of the radio ect. Do a radio check, and on water test, check for leaks and condition of hull for cracks ect and also pay attention to the transom area to make sure it's still strong. Also check the fuel breather is not blocked. Check nav lights and all saftey gear is there and working and in date. pay attention to the trailer and make sure brakes work and wheel bearings are good, and rollers support the hull properly and the lights work.
Best I could do off the top of my head.... but I don't even own a boat, so it may all be gospel.