Depending on how you use your rig, this could be an endless list. That said, here are a few items I've found make like easier:
Bungee Cords - various lengths. Can be used for a multitude of tasks.
Zip-Ties - various lengths, usable for many things
We all know what they are... for things you want to secure permanently.
Gear Ties - again, various lengths & colors. Flexible rubber-coated metal ties. Think of these as twist-ties on steroids. I find these better than velcro for securing most anything, but don't necessarily want it to be permanent.
HoseGrip 2: https://rvcablegrip.com/Index.html
While most water hoses have a decent grip on the end to connect to the RV park waterspout... if you also use a pressure regulator (and you SHOULD!), they don't. Adding this to the end of the regulator makes connecting & unconnecting much easier.
(If you use coax for cable tv hookups, check our their coax-cable grip-connectors too)
DuraFlame Logs: If you like a good campfire, and don't wanna spend all day trying to get it started... use these for cheats. I cut a standard log into 3 pieces, and toss 1 into the fire pit along with my firewood. Easier than scrounging around for kindling wood, and cleaner than using cardboard (less flying ash).
Firewood "grenade": Speaking of campfires... often the firewood you get at campgrounds are large pieces that won't burn quickly. Using one of these makes spiting them into smaller pieces quick & easy. A few blows from the hammer end of a hatchet is all it usually takes. I call them 'grenades', and they can be found on Amazon or Northern Tool, etc.
Surge protected power blocks: RV's never seem to have enough power outlets. Using a standard extension cord will work in a pinch, but why not have surge protection too?
Finally... Zip-Lok bags - various sizes. I use 'em for everything.