Trailers should be checked before use as well. Being parked on the side of the road because of a flat tire or a bad wheel bearing really puts a damper in the weekend boating excitement. Lubricate and inspect the hitch coupler. Safety chains might keep the trailer from getting away from the vehicle when the coupler comes undone, but why have that happen in the first place. The coupler needs to be free to move but at the same time fit tight over the trailer hitch ball.
Check the air pressure and inspect the tire treads and sidewalls for cracks. Low pressure can cause the trailer to start swaying and potential cause the loss of control.
Inspect the bearings and repack if necessary. Don’t rely on just pumping more grease into the hub. The bearing should be cleaned and repacked at least once a year or so. Bearing greasers do help keep water and air out of the hub, but over time the grease gets heated and hard and doesn't provide the lubrication it needs to. The only way to prevent damage is to clean and repack the bearings. If you use the trailer in salt water, check to make sure you can flush the hubs and break to prevent corrosion.
Extras are personal flotation devices, safety equipment and paper work. Remember; don’t leave home without it means more than the boat. Make sure you have a enough personal flotation devices for the rated number of the boat or at least for the number of people that you take with you.
You’ll want a safe and dry place to keep the registration and insurance paperwork.
You also want to make sure that all of your fire suppression and extinguishing systems are fully charged and in working order.
If there are inspections required, make sure they are done before you head out on the water.
One other thing to think about is having a good Marine First Aid kit.