In my Jeep I generally Keep 1 extra set of clothing (rain / cold weather gear included) as well as a few tarps, wool blanket, sleeping bag, several knives, lighters, flashlights etc. All of this is in addition to what I plan on needing for the trip. Officially I carry these as personal backups, but I find that I am normally prepared enough not to need them. Thus I normally end up loaning my redundant gear out to my friends.

My friends tend to be rather ill-equipped on our outings. Lately I've been packing a few additional items which are slightly more PHRASECENSOREDPOSTERSHOULDKNOWBETTER. friendly. For example I now keep a spare folder in my Jeep to loan out in addition to my emergency Ka-Bar. I like to save the day and help out my friends, makes me feel like a hero

On my last outing, one of the tents was not pitched properly and the occupants got wet during the night. The next morning, when I found out, I asked if they were ok, and if there was anything I could do. She said her gear was soaked, but doubted I could do anything about it. I responded by pulling a full set of Gore-Tex rain gear out of the back of my Jeep. The expression on her face was priceless