Water pressure regulator - Essential...don't hook up without one.
50 -30 amp adapter - Very rarely needed, but for under $20, a good item to own.
Surge protector/voltage regulator - almost essential. Get a P.I. 30 amp unit,either hardwired or portable. Much cheaper to buy and use rather than face cost of repairs after plugging into one bad power supply. If you are a gambler and with lots of $$, you don't need one. Otherwise, consider it a part of the cost of camping with the amenities of a fridge, 120 volt power, television, etc.