Stuff I carry in mine:
Generator.
firewood and chainsaw (occasionally)
Extra water on long trips, or remote camp sites.
Motorcycle (or two), but not on all trips.
lawn chair(s)
patio mat
fuel for generator and motorcycle.
stuff such as extension cord, extra hoses and other doo-dads to set up around camp.
My truck has about 35,000 miles on it now. At least 25,000 miles of that have been traveling with the camper on it. Truck and camper were placed in service as a camping rig in early 2010, I don't daily drive the truck.
Of all the trips with the camper on, only 2 or 3 have been without a trailer:
1. Feb 2010 - Drove from Tacoma, WA to Eugene, OR to AM Solar to get the solar installed.
2. Last weekend I drove from Spokane to Tacoma for a show without the trailer - the trailer was already in Tacoma from the weekend before when I towed it there with my other truck.