Here's what's in my trunk boxes (from memory...I'll check the box when I get home and edit if needed)

1: A box: Plastic with a lid that will keep water out if rained on...inside of which is the following:
2: Belt Knife (one of my many surplus sharps)
3: Multitool
4: AA LED Flashlight (with batteries reversed just in case)
5: Hand crank LED flashlight/radio/cell phone charger
6: Duct tape
7: Folding Shovel
8: Stainless cup for scooping/cooking/whatever-ing
9: Esbit or canteen stove
10: 24 Hexamine tablets
11: Mechanics gloves
12: First Aid Kit
13: Glow Sticks
14: Hatchet/Axe (One box has a Trailblazer pack hatchet. My Jeep always has an axe in the back besides the box)
15: Bic Lighter AND a jet style butane lighter
16: Lifeboat matches in waterproof container
17: Tinders (waterproof)
18: Food (cans of soup and some snacks)
19: Water purification tablets
20: 12V tire air pump
21: Booster cables

Then I have a jumbo size Ziploc storage bag (the smallest of the super jumbo storage bags) with:

1: Blanket (The $10 kind so I can use it to crawl under the car to work if I have to without getting too dirty)
2: Wool gloves
3: Neck warmer/head over
4: Toque
* In summer I'll swap out the 'warm clothes' for just 'extra clothes' so I have something to change into if I break down in my nice work clothes and need to spend any amount of time somewhere.

I also have the obligatory tool kit which has all the repair stuffs. Mine are in need of overhauling...something I need to do before my next big road trip.