What the others said, plus a couple qts of oil. Definetly the toilet paper. If you can find it, get some Rescue Tape, there are other names for it also. It is a silicone rubber type material, that only sticks to itself. You can use on radiators, gas lines, electrical connections, etc. If you get oil on it, just turn it over, and use the other side. There are no adhesives on it. If you need an O ring, just wrap it around an appropriate size dowel, etc. and then roll it off, and you have an O ring! Really amazing stuff. Harbor Freight used to carry it but now they have something else that is a cheap copy of it, and isn't any good. Also, if you have a Harbor Freight near you..... The Man's Store....
Look for the sales, and you can get a 2000 lb. pull winch, with fair leads, and remote cables, for $49.00 on sale, and a little more not on sale. I keep one in my truck, plus a tow strap, and a tow cable. Definitely extra ammo, and a couple boxes of .22's. I keep a couple of tire plug kits, plus a little air pump, in a bag. A little box, wood, metal, Tupperware etc. to store the stuff in. It is real comforting to know you have those things when you are 20 miles from the nearest highway, let alone any town or gas station or parts place.
Something to add to your first aid kit, is a roll or two of co-ban, elastic bandage. You can get it much cheaper by going to a feed store and getting a couple rolls of leg wrap. It is the same thing, only it comes in colors, and is about three times wider than a normal roll of co-ban, and is cheaper than co-ban! You can cut it to the width you need! A single roll of co-ban costs about $4.00, but a roll of leg wrap is about $2.90 or so. It is great for splints, wound wrapping, wrapping feet for blister protection from ill fitting boots etc. Some rain gear, extra socks, boots, or shoes. You get stuck, broke down, it is nice to have a change of clothes, oh a bar of soap, and a little or bigger bottle of hand sanitizer. Good for starting fires too. Just don't have any on your hands when you try to light a fire. A little pack of bick style lighters are always handy to have along. A small, qt, to qt and a half sized metal pot to cook in, and or boil water. Chop sticks, knife, fork, spoon. Those little bottles of your favorite seasonings. Salt, pepper, Mikey D's and Booger King have those little salt and pepper packets, and ketchup, mustard packs..... Free!
Yellow mustard is a great home remedy for painful gas! A spoonful, and the gas pain is IMMEDIATELY gone! A small shovel is mandatory! The handy man jack or whatever you prefer to call it is great. It can be use as a winch, or come along also. I have the one my Dad bought when I was a little boy. Yeah, you had to be careful of flying handles. Bolting them in was always a good idea. They pretty much have you covered, Anyway, enjoy your truck! Oh, yeah, a portable Holiday Inn (sleeping Bag, maybe a self inflating air mattress) I have those in my truck. People ask me why I carry all that stuff, in the back of my truck. I ask them ever break down, or get stuck in the middle of no where, and no phone service? I put a lot of miles on my truck. I know that if I have a problem, I am able to last for awhile, and fairly comfortably. Oh, a good little hand held GPSS, or a car mounted one. If you have an emergency, and need help, and have phone service, you can give your GPSS co-ordinances to help in locating you, and extra batteries.
Wayne