A good trick to knowing what you should have in an emergency bag is by going to a site that sells them. Looking at what they put in their bags and copy it. That's what I did.
Emergency essentials sells a ton of bags designed for different needs. In car, home, # of people, length of days.
Well I have my truck fairly well packed for any occurrence.
The usual (?) car care necessities : tools (pliers, vise grips, hammer, screw drivers, extra huge screw driver, wrenches etc..) transmission fluid, oil, jack, fix a flat, jumper cables, tow rope, tire pump, rubber chocks, spare tire (in good shape and full of air), lug wrench, WD40, ice scraper, long metal tire iron (to pry with), tool bag
Then some (!) extra stuff like: Two tanned lamb hides that use for seat covers, several big lawn size trash bags, several ziplock bags, zip ties, duct tape, small roll of wire, electrical tape and wire nuts (various sizes) a emergency mylar blanket, an emergency fleece blanket, rubber boots, socks, winter hat, extra jacket, 50 foot of mountain climber rope (fastening loads) a couple of rolls (50 foot each) nylon cordage, several different kinds of snaps, Chicago screws, several pre-made rope ties for tying small things in the truck bed, bungee cords, 2 rolls of florescent plastic ribbon (to tie on loads or make markers from), 2 flash lights, emergency compass/whistle/mirror, fish hooks, dental floss, hole punch, twitch, 2 knives, 3 to 4 canvas tote bags (my grocery sacks) 3 collapsible mesh laundry hampers (what I haul stuff in so it doesn't rattle around in the truck bed) two plastic tote bag things (what most of the other stuff is stored in behind my seat), 2 large rubber backed rugs, 1 or 2 bags of match light type charcoal, long reach lighter, cotton leg wraps, salt, pepper, mustard, extra straws and napkins, a good book, aspirin, my meds, bug spray, lip balm, sunblock, usually gum, mints and snack of some kind, usually a big iced down drink (coke) that I never leave home without. I recently added a couple bottles of water. Oh and my insurance card!
Believe it or not all of this "stuff" fits either behind or under the bench seat of an old Chevy pickup and I can still fit myself and a couple of passengers inside!
This is NOT really survival stuff - just stuff I need. After reading this I think I may have a problem.
We have bug out kits. They contain the expected things, first aid kit, water , MRE's ( yeah I know Yuck, but it will do the trick) Blankets and socks ( nobody likes wet socks). They also have maps, compass , crank radio/flashlight, various tools, a good hunting knife, rope , waterproof matches and a butane lighter, sleeping bag ( or bed roll ) water purifier tablets, road flares, and several other things that all fit neatly in a back pack. I know it might seem silly to some folks, but we have actually put some portions of them to use. Stuck in traffic and sweet husband blood sugar crashes, flat tire at 3am in the middle of nowhere. (that one inspired the addition of a can of Fix-a-Flat and playing cards) I would much rather have it and not need it than need it and not have it.
Its funny you should start this thread...I just got my bag out of the truck, to refresh and replenish it, the other day.
I guess what you have in your car, depends on your location. Here in IN, the winters can be pretty cold and snowy. I ALWAYS carry a blanket, flashlight, jumper cables, fire extinguisher, tarp, and tie down straps. I also have a few other things in there, medical type stuff, for "just in case".
Hubby gave me his shaveing bag from when he was in the military..and it fits quite a bit in there, and its compact.
When we were stationed in Alaska, the military recommended we always have peanut butter, and crackers in there as well.
If you live in a cold area you should have something to keep you from freezing to death. I carry matches and 6 long burning candles. Candles can heat up a car enough to save your life. You should have more than just a blanket, like down or wool blankets that should be applied as soon as you know you are in trouble, don't wait till you are already cold. A stash of those gel plastic hand warmers can be used for feet too and placed on the belly for core heat also. 4 for each person that the car might carry. spare gloves is smart too, which I don't have...
I have a full on pharmacy in the car. Chewable children's motrin, chewable children's anti-histimine, a childrin's epi-pen, (guess what our biggest concern is?), a whole arsenal of band-aids, guaze, instant ice-packs, etc. I've also got my personal medications in there. I go through it regularly as well to make sure it's up-to-date non-gunky. It has come in very handy over the years. This is in addition to all the regular "keep the car running" stuff like extra fluids (oil, transmission, etc). Also a change of clothes and diapers for the little one, and things to keep the kids occupied. Probably a lot more as well, I tend to over-prepare.