Interesting question, and I think the only real way to find out is trial and error.
No matter what tools I have (and I have a LOT), whenever I get a new vehicle, I end up needing something new.
So what I do is start out with a basic kit, and add specialty tools as I go.
My basic kit is my mechanical tool bag that I use at home and at work. It contains, in no particular order:
Ratcheting screwdriver kit, with regular sized bits and smaller precision bits. Torx, phillips, flathead, and hex.
Crescent spud wrench
Small and large needlenose pliers
Small and large phillips screwdrivers
2 Channel Lock "awesome wrenches.
http://www.amazon.com/Channellock-Code- ... B001BPYPOK Do yourself a favor and buy a couple.
Set of Metric and Standard nutdrivers.
Small torpedo level
Hammer
Tin snips
Large, medium, and small vice grips
2 pair small needlenose vice grips
Fine and coarse tooth half round files
Rat tail file
Needle files
Large and small wire cutting dikes
12" Bolt cutters
Leather work gloves
Pack of Irwin utility blades. No other brand is worth buying, BTW. Won't break, won't bend, stay sharp.
Metric and Standard Gear Wrench Quadbox: Again, do yourself a favor and buy these:
http://www.gearwrench.com/catalog/wrenc ... g/quadbox/Metric and standard combination wrenches
Large and small channel locks
Set of folding Allen Wrenches, metric, standard, and torx
1/4, 1/2, and 3/8 ratchets, with metric and standard shortwell and deepwell sockets
25' tape measure
Husky utility knife
Several small and medium crescent wrenches
Pen, pencil, Sharpie
Dental picks
Tapered and straight drifts
center punch
cold chisel
Several flashlights and a headlamp
As I said, this is my work bag. I often have to lend tools to my climbers, so there is a lot of overlap.
One thing I like to do is organize everything in small tool envelopes. Husky makes some good ones. This way, I can have specialty tools in the car, at home, etc, that can be plopped into the main bag as needed. I have a car bag, an electrical bag (multimeter, connectors, electrical tape, wire, soldering kit, etc etc.). It also lets me find tools quickly in the dark, since I always put everything back in the same spots or envelopes.
In the car, I keep an emergency box with pump, plug kit, jack, towchains, shovel, etc.)
Still, the basic bag gets most things done with no muss, no fuss.
EDIT: forgot to mention: BUY QUALITY!!!!! A tool that breaks when you need it is worse than useless, it's dangerous. Think of your tools as lifesaving equipment, and budget accordingly.