My truck kit contains vehicle-type survival stuff, including a combo battery-pack/air pump (Never mind booster cables, these don't need a second vehicle), tow strap, tools, strobe lights, and other safety gear. I also have a separate bailout bag in it, equipped with everything except a gun. In the winter, I throw in a large duffel-bag survival kit with cold-weather gear, food, etc. for two people. If the winter looks really bad, I throw in snow shoes, too.
The real secret is you don't want a survival kit, you need several. First, you don't know which ones you'll be able to grab. Second, redundancy never hurts. Third, you can add extra capabilities to different kits. The more kits you can grab when TSHTF, the better off you'll be.
I recommend this book:
