Every kit needs to be adapted to your specific needs. There is no right or wrong kit.
Here is what we use:
1. Flashlight. I have a light that I can wear on my head to make it hands free.
2. Miniature first aid kit: Pepto Bismal, Motrin, tweezers (splinters), band aids, children's Motrin (liquid), feminine supplies
3. Collapsible army shovel
4. Wool blanket and space blanket
5. Jumper cables
6. Two "Beenie baby" stuffed animals (in the event of an emergency we can share these with our children or other children to provide comfort-put in a plastic bag to stay clean, dry and smelling good)
7. Fire extinguisher (ABC)
8. 10x12 cheap plastic tarp (from Wal-mart, used for laying on the ground under the car or kneeling on to change a tire)
9. Granola bars and crackers and 1 gallon of water
10. Tow rope
11. Duct tape
12. Hand warmers
13. Phillips and regular screw drivers, pliers, knife
14. Winter cap, scarf, socks, gloves and rain poncho
15. Umbrella (rainy day)
16. Bungee cords (carry something larger than the trunk, allows me to close trunk)
17. Baby wipes (children always have a need to
18. Clean rag (serious wound, spill in the car, or keeping hands clean)
19. Siphon kit (Harbor Freight-in case I have to siphon gas).
20. Funnel (used to pour fluids into the car without spilling)
21. Leather gloves
22. Small empty gas can
22. Can of Fix-a-flat
23. Ice scraper
24. I also have a breaker bar with socket size already fitted exactly for my lug nuts even though the car comes equipped with a little bar supplied by the manufacturer, the breaker bar is much better.
25. Kitty litter (Used for ice, I don't carry it, but many people swear by it)
26. Member of AAA
This seams like a lot, fills half the trunk and is bad for gas mileage but its nice to be prepared.