Some blogger, I think George at Mad Ogre, did a post about a backpack.
I ordered one from Amazon for around $35.
On my F-250 there is a cross bed tool box from before I retired from pushin' construction projects.
In the main compartment of the pack is a poncho,
3- pair of socks
2- pair of underpants
3-bottles of water
and room left over.
Second compartment has #1 med kit (gun shot, lost limb, etc.)
1-roll of tp, flattened
3-packs of kleenex
1- #2 med kit ( booboos, owies, etc.).
1-Garmin GPS w/extra batts
1- GI compass
1- cheap GPS
5-zip lock bags
1-box wp matches
2-small led flashlights w/extra batts.
In the fifth compartment;
4-packs of instant coffee
3- 50' of 550 cord
1- small bottle of diesel, (good fire starter)
5-beef bullion cubes
salt, pepper, handiwipes, Motrin.
On the outside is a canteen w/cup and a K-Bar.
All of this is in that pack with a little room left over and weighs 15 pounds.
In the truck box is a 10'x8' tarp, tools, large spool of 550 cord, 50' of 3/8" rope, a sleeping bag, 1gal can of diesel, a case of water and an AR 5.556 w/4 mags*.
(*Only on a planned trip to the sticks)
If that won't get me home, I'm jackin' the next guy by.
The pack will be replicated for her towncar which has a bitchin' area under a lift lid in the trunk.
Firearm is my EDC, usually a 1911 and two mags.