I have made it to this point in my life with a few basic tools. I don't want to list them all, but everything but my cordless drill, jack stands, oil pans, funnels, and jack fit in to a small black tool box and a blow molded craftsman 115pc tool set.
Up until I bought my house last month, it all fit neatly in the trunk of my car and was always with me. Now that I have a garage, I don't much care for hauling them around.
My vote:
-Drill
-Set of open and closed end wrenches (standard and/or metric depending on your needs)
-Screw driver set (various sizes and lengths of phillips and flat head)
-1/4", 3/8", and 1/2" Ratchets of varying lengths
-Standard and Metric Sockets for above ratchets
-Set of Pliers (Various sizes, styles, and lengths)
-Standard and Metric Allen Wrenches
-Popular sizes of Torx bits/drivers
-A set of impact sockets (standard and/or metric - even if you don't have an impact gun - see next item)
-Breaker bar or "cheater bar" (Use impact sockets and a ratchet with a lifetime warranty in combination with this)
-Small Hammer
-Medium Hammer
-B.A. Hammer
-Hand held torch (or better)
-PB Blaster (it is a tool in my book - I always keep a can around)
Can you see where my list is heading? I own a car that lived the greater part of its life in the north-east. Now that it is in KY, I have learned how to remove rusty things quite well.
There is more than I have listed that I probably consider very important, but it is late, I am at work, and I must move on.