It's a long story, but in short, I drove a girl home who had blwon two tires, after a friend and I put her spare and my spare on her car and got to thinking she had too much to drink to be safe making the 30-40 minute drive. I haven't seen my spare since, but I did get a flat. It was then I discovered the beauty of fix-a-flat. I've got two tires on that now, I live just out of town and people pick stuff up out here, and after several thousand miles they're both still going strong! I keep a spare can in my trunk nowadays, anything less than a blowout and fix-a-falt is just shy of a miracle!
Anyway, fast forward to today, me and my friend were doing an oil and filter change on my car, but all he had was inch sockets and I needed metric. I almost got a Stanley set for $17 at WalMart, but I really didn't want to spend more than ten since all I needed was a 14mm and 10mm. Well, I went from tools down into automotive, and lo and behold they have a glovebox socket set, full compliment of metric and inch, plus extension and ratchet, for a measely five bucks! Yeah, it's totally generic, Tawainese import junk, but it did the trick and can't beat the price. Kinda a shame, though, I'd much rather if it were American made, even if it was robots doing the labor.
Distilled water is good to carry, at least a bit, since you can drink it or use it to refill your radiator. I have a large piece of tire cloth, probably the better part of a century old, handed down from my great grandmother who was a cork and rubber worker. The stuff is still going strong and makes an excellent ground/drop cloth and also blanket. I have a 2 ton hydrolic jack and 4-way lug wrench that will tackle metric or inch lug nuts.
Definately best to cover mechanical failures before killer mutants on this one. Tires and radiators seem to be the big ones to go, but it might be a good idea to pack some gas line as well. Preventive maintenance is everything. My car's 17 years old, bought it for $500, and in the spirit of Pulp Fiction "aside from the way it looks, the car's cool."
Anyway, I don't travel without my little knife, my big knife, my custom CZ 75B, at least two loaded 16rd mags and 200rds CCI Blazer hardball. Just in case. There aren't many routes I take that are too far out of civilization, but if it came to that this is boar country and I do like some pulled pork bbq... hmm... I think I'll keep some bbq sauce in the trunk from now on...
BTW, if you pay somebody else to change your oil, you should consider doing it yourself. I use the synthetic high mileage stuff just so you know, but it costs me $40 at least to get it professionally done. Doing it myself costs about 14 bucks. You'll pay a certain ammount for an oil pan, funnel, $5 Walmart ratchet set and oil filter wrench, but that might be $20 bucks one time cost. Premium oil is $2 a quart, my 1.6L 4-banger takes 3.3 quarts. Winchester 9mm Filthy Pack is $11 for 100rds. That's 200 more rounds down range every couple months, for free, just from taking half an hour to change the oil myself. And it's so easy anybody can do it. The used oil goes back to the autoparts store in the bottles the new oil came in.