Oh, nobody will believe this, but here I go anyway. Maybe I'll post pictures to prove it.

1 Full Set Firefighting turnout Gear (pants, jacket, boots, hood, helmet gloves)
1 ANSI Class 3 Rain Coat, Lime Green
6 Highway Traffic Cones
1 20 LB ABC Fire Extingisher
1 4x6 Wool Blanket
1 Large First Aid Kit with Splints and so forth
1 8x10 Tarp
250' 10mm Rescue Rope
6 Carabiners
2 Figure 8 Decenders
2 4" Pulleys
8 4' Lengths of tubular webbing
1 Full Change of Clothes & 1 Spare Pair of Shoes
12 30 Minute Road Flares
1 Air Compressor
2 1000 lb Ratchet Straps
1 hand Tool Kit (misc tools, some supplies)
Assortment Bunji Cords
1 Car Jumper Battery Box
Nylon Vehicle Recovery Strap
1 Life Jacket equipped with strobe and gerber fixed blade knife (for Marine Rescue work)

Also in the car is a fully packed North Face Recon Pack, which I use on SAR jobs and so forth. It's a combination 3-day kit with some additional navigation items in it and some specialty gear that I need for the fire department. I can't remember the full set of what's in it right now, some highlights are:

2 Liters of Water
4 MRE Main Meals (Just the meal pack, not all the extra stuff)
Silva Compass
Magellan Meridian Color GPS
Topo Maps of the state parks and State Game Lands in this area (waterproofed by soaking in Thompson's Water seal and hung to dry)
A Blaze Orange Vest (for when we have to search game lands)
250' of Orange Para Cord
1 Space All Weather Blanket
1 AMP First Aid Kit, re-packed into a small Pelican Case, som additional items
1 Pair Motorola GMRS Walkie Talkies
16 Lithium AA Cells
Sweetwater Filter/Bottle
Light Duty Polar Fleece Sleeping Bag
2 Large Contractor Garbage Bags
1 Air Horn
3 Small Flares
Firemaking Stuff (matches, tinder, sparkers and such)
Eclipse Attitude LED Light
Pens and Pencils
Waterproof writing pad

There's more stuff in there, mostly small stuff. Flashlights and whistle I have OMP all the time, so that's not needed to be packed.

Addtional radio gear sometimes comes along for the ride - mostly fire department HT's.

Not to start another firearms debate here, it' s just that I saw firearm on another list....I'd carry a firearm of some sort if it weren't for the fact that I'm directly on the border between the United States and The People's Republic of New Jersey and cross over the border all the time, mostly to shop and such, but fairly often on mutual aid fire/rescue calls. Even thinking about firearms in your car in New Jersey is a crime, much less actually doing it. I used to carry an unloaded, dissasembled M6 Scout in the truck, advice from a NJ state trooper told me not to do it any more, because the ammo stored in the stock makes that a "loaded weapon" (as does a magazine, detached from the gun, but loaded with ammo, make a "loaded weapon").