Are you asking contents, or bags/boxes?
I would be using a soft bag... so you dont have to ditch the empty container when no longer needed.
for contents:
Box Wrenches (Metric or standard depending on your car... unless your thinking you need to help someone fix their pre-87 American car.)
Adjustable wrenches! Big, and small.
Vice Grips. For stuff thats not a bolt... that needs to be loosened!
Needle nose pliers, for pulling thorns out...
Pliers... for swapping out oil filters (Your not gonna have anything you can recognize as an oil filter after its off... but they'll do the job.)
Electrical wire strippers/crimpers. A pocket knife works to cut, strip, and if its a leatherman... crimp some small stuff! A real stripper/crimper does the job at hand right.
A decent file... cleaning up bolt heads so you can get the socket back on em after you booger em up with a set of vice grips.
Sockets (1/4 3/8 and 1/2) Short, and deep. With ratchets, a 1/2 inch breaker bar. With pipe. (about 2 feet long... make it heavy and its self defense!) Extensions for each. Flex adapters... so you can get in to tighter places! Spares of 10mm for metric... and 1/2 and 9/16.
You will want some latex/nitrile gloves. Some roper style gloves in case you have to deal with something hot.
Duct tape (the real stuff...)
-A couple raps around a V belt (not serpentine systems...) will work for awhile in place of a fan belt.
-A bunch of raps with a soup can/soda can slip fitted around a broken radiator hose will fix a blown hose. Short term.
-Holds car doors closed... rap around the posts!
Electrical tape (again... not the cheap stuff.)
Bailing wire (or other maleable wire... useful for all sorts of stuff! 20feet or so... it coils up. Use some tape to hold it in its coil.)
Cutting shears/tin snips. If your car has metal body panels, these could come in handy for trimming fenders after accidents... where a hammer just wont work.
Speaking of hammers... a claw hammer, with a metal handle. This is your short pry bar... and hammer for non-hardened metal. You'll also want a ball peen, you decide on the size!
Epoxy puddy for fixing holes in fuel tanks.
Tool to replace fuel filter if you have a late model... and replacement fuel filters. Crappy fuel, is not something you want to be stopping you. Even if it means you have to swap out a filter every 30 minutes.
Jumper cables... self explanatory
Spare lug nuts... studs if you have them. Try to find a car that is lug centric, not hub centric. That way either the rim or the hub can get beat up... and as long as most of the studs are in shape... your still mobile.
A tire iron. You want a 4 way. You want to check the torque after the tires get swapped out with a torque wrench. Quite a few shops put the lugs on with an air gun... you dont want to have to loosen them! (I've had to put 3 foot pipes on breaker bars to loosen em up. Standing on them! I'm around 190lbs, if that says anything.
Brakes... lets hope you dont need to jury rig the brakes.
Ignition, if your vehicle is serviceable (Older than OBDII) on the road, you'll need ignition components like distributer caps, rotors, points (if you have em...) spark plug wires, and plugs. Stay name brand on this stuff... good stuff lasts a hundred thousand miles... cheap causes mis-fires and a poor running engine.
Depending on if your urban or offroad... you may want to keep oil on hand for your engine and transmission... JB weld and some sheetmetal plus a couple rivits can put you back in buisness. The differentials... well, normally they dont need to be serviced, but if you have to ford water deeper than the breather, you want to swap out the oil in them.
Its up to you, but carrying oil and filters for the engine... enough water to fill the radiator (along with anti-freeze...) in a non-mixed fashion (water supplies!) and transmission fluid... you can! If you have a small car, your taking up a good bit of cubic volume with these. You might be able to stash some of this stuff under the hood by building a box under the hood. On older cars (When fenders were fenders...) you might even be able to carry your oil and other goodies inside them... some fabrication work needed to build boxes to keep em secured, but not impossible.
Under the seats especially rear benches (SUV) is another place for some plywood boxes to hold some stuff.
I highly recomend some plastic sheeting and carpet... 8 feet long by 3 feet wide on the plastic give or take for your size, and 8 or so by 2 feet with the carpet. Instant creeper... lots easier on the back than concrete/asphault or rocks! A real roll around creeper takes up to much room in my opinion to carry around!
Tire plug kit. Possibly the MOST important part of this kit. Without tires that hold air, you dont roll. You need one of these little fixits, along with the slime ya use to plug the hole.
Air pump. I have yet to find a decent hand pump... if you find one that can pump a tire up to pressure, please post a link! Some air is better than no air...
Theres alot missing from this list... but, its a start.
Up north... Maybe a shovel and some trashbags. More traction for pickups... shovel in some dirt for the bed... bag it though! its a pain to clean dirt out of trunk carpeting if your driving a car!
