I didn't see you mention anything about a small bottle jack. That takes virtually no room at all and can be used on the truck and camper. Also, I recommend taking 1 or 2 light duty (14GA) extension cords, 25-50 feet each.
One other thing (and I might get laughed at here), but I assume your hybrid trailer is a single axle and very light weight...so carry some HEAVY DUTY zip ties. You might be surprised to know that, if you had a leaf spring/axle u-bolt break, you could actually provide enough TEMPORARY support with 4 of these zip ties in place of the u-bolt...enough to let you limp to the nearest exit/rest area.
Generally speaking, I think there's really no limit to the amount of small things you could carry along. If you have a small tool box that you take anyway, just make it sure its 100% full to the brim of anything you could think of. In other words, if you have a 10x20 box, it takes up the same amount of space if its empty or full.