Couple things I'd suggest:
Your safety vests - there are very specific requirements now for reflective area so make sure they are current models because some of the old small size ones had too little area to identify on a thin framed person in low light!
Fluorescent glow sticks - a must. Dead flashlight batteries happen and figures it would happen the time your TV's alternator craps out and you've drained it and the trailer battery unknowingly. You should have at least two flashlights too regardless - one for you and one for your spotter.
Triangles are great, but get a pack of flares. Unless you know how to properly set them out (spacing versus size) their warning isn't as attention getting as burning flares. Further, triangles, especially lower grade ones, are practically worthless in pouring rain!
How about the jumper cables? Spare drive belt is cheap insurance. Air filter (ever go down a long dusty road in the middle of nowhere in the summertime with your camper in tow)? How about a tire plug kit because multiple flats happen (even if you have roadside assistance, they can't always get to you for better than half a day or the next)?
Add to your assorted wrenches a torque range in a range for both your lugnuts and the required torque on your hitch ball and bracketry/connectors of your hitch.