How much wrenching are you gonna do roadside anyway? Especially these days where a car's engine centers around a computerized control system. Unless you're packin' along one of those scanning computers and all the manuals, you wouldn't know where to start? And unless you're carrying a NAPA store in the trunk, you're not gonna have parts anyway.
If you're car like most these days has one of these serpintine uni-belts, you can, for about $50, carry a spare belt. It's very small and very light-weight and will probably back in and around the spare tire. And the belt is easy to change on most cars if you know the pattern which is often printed on a label inside the hood. If not, photocopy the diagram out of the owner's manual and stash it with the belt.
I suppose you could carry a spark plug for some cars and replace one of those. But what are the chances of a plug going bad? Well, I should talk. My car had a plug replaced a few months ago. But a spare plug for my car would cost $350 and it's not exactly something you can change in the field anymore. $350! for a spark plug!?! Yup. Fortunately, mine was well within its 150,000 mile warranty. On my car, the whole ignition electronics, the coil, condenser, etc., are now integrated into the spark plug as one assembly which elliminated the spark plug cable. I have, over the years, replaced more spark plug cables than spark plugs. And these new plugs are supposed to go 150,000 miles. So, so much for carrying a spare spark plug.
You can top off fluids in the field. If you suddenly come up a bit short on coolant, probably a slow leak somewhere, maybe a cracked water pump, you would top it off enough to keep driving until you can deal with the problem. But you don't need much along the line of tools to top of fluids in most cars.
Several years ago, when I was still driving my old Olds, the charging idiot light came on. The charging system in this car was basically all integrated into the "generator" assembly. The diodes, the regulator, everything was in that one assembly. And there it was, right on the top of the engine. Held on by just three bolts. Two cables connecting to it. I can do this myself! So, I went to the parts store and bought me a part. I got home, took the belt off, disconnected those two wires, removed them three screws, and the danged thing would not come off. I got to lookin' and sure enough, there was a fourth screw underneath. No way you could get to it. You'd have to take off this whole bracket with all sorts of stuff attached to it. So, I put back the three screws, reconnected the two wires, put back the belt, and drove to the dealer. As I got out of the car with my part in hand, the service manager smiled knowingly, "Generator, eh? Tried to do it yourself did ya? We see a couple of these cases per month. Have a seat in the waiting room, this takes about 45 minutes."
"Ok, but how do you get that thing out? Just tell me. I'm curious."
"The GM Manual calls for removing this here bracket. But look at everything you'd have to disconnect. That's the AC Compressor there. And that's the steering pump there. The GM guidelines say this job takes five hours."
"How do you do it in 45 minutes?"
"We remove the front two engine mounts and use an engine hoist to tip the engine up so we can reach underneath. Don't worry, we'll only charge you for 45 minutes of labor."
"Go, go... get tipping."
So, unless you're carrying an engine hoist in your tool kit, you can't even replace the generator, three -- no four -- bolts and two wires, in the field.
You could patch a hose that's sprung a leak. I did one of those myself not to long ago. But all you need for that is a towel and some Windex (tm) to clean the hose off so that the tape will stick, and then a roll of hose tape.
So, the question now becomes: Why should I haul around a hundred-piece mechanic's tool set that weighs 30 pounds, when I'm really not gonna be able to do a whole lot of major repair work in the field anyway?
