As usual, Schutzie is late to the party and all the good stuff has already been taken.
You have a repair kit for your boats, and a tool box for your cars; you need one for your trailer. From painful and expensive experience, a repair kit for your trailer is as important as beer. Include stuff like spare bulbs, electrical repair clips, duct tape (duh) bearing grease and spare bearings. The bulbs are especially important if you have Colorado tags and are traveling to Utah or Wyoming; a burned out $1 bulb should not be the basis for an expensive and time consuming search of your entire world. Spare lug nuts, whatever you can think of. An old no longer waterproof ammo can works nicely, can be welded to the trailer, and locked if you modify it slightly.
Second; bearing buddies.
Third, clean and repack bearings at least annually.
Fourth, check those lugs, the hitch and the connection regularly, like every time you stop for gas. Or when you cross the Colorado border.
Fifth, practice backing and parking the trailer before you head out. Better to embarrass yourself in the local school parking lot than at the ramp when you're trying to impress everyone with your equipment and skills.
Sixth, yes, disconnect your trailer lights before you back into the water. You won't electrocute yourself if you forget, but hot glass bulbs do not mix with cold river water well.
Seventh, do not overload your trailer.