In addition to the stuff already mentioned, spare, etc, I’d reiterate the extra set of bearings and all the tools to change them on the side of the road. Punces, BP hammer, paper towles, grease, etc.
I also throw in a couple of sets of disposable work gloves, so if I have to change a bearing or do anythin else with grease, I can wear those and then throw them away later.
I’m also a big fan of having some of those ratcheting tie-down straps. You’d be amazed at what you can fix with those. Busted weld on a trailer frame? Yep. Broken leaf spring on trailer? Yep. Heald together with a couple of those straps.
Other items I always have: Sportsmans Goop adheasive, JB Weld, duct tape, two long tow straps with schackles, two working flashlights with extra batteries and a headlamp.
Grouse