Snap-on (there is a difference!) left-hand drill bits and extractor set! These really make life simpler removing rust/broken bolts. Really nice to just put that left-hand drill bit up to a broken bolt and pull the trigger on the drill and out comes the broken bolt.
Hot Wrench, i.e. Oxy-Acetylene torch. Nothing says F-U stubborn bolt like cutting it right off. A torch really makes parting out, parts vehicles quick and easy! Just cut stuff off!
Dove-tail dual axle trailer - can't believe how many times I've used my trailer! For both the good times and the bad times! Picked up a few projects with it. Only down side is if your friends know you have a trailer (and truck) you will be on their speed dial to help moving anything - house, furniture, Bronco, broken down vehicle, air-compressor they just bought, kid(s) going to college, divorced wife, divorced husband, whatever!
And on the flip side of Snap-On tools, cheapy tools. Anything Harbor Freight. Yes, they are cheap Chinese junk, but if you think you'll only need a tool once, it's a great place to pick up cheap stuff. They are a piece of junk, a guaranteed piece of junk! I've found Harbor Freight to be fairly generous in their exchange/return policy on broken stuff too. (I wish all my tools could be Snap-On, but I'd be dead broke.)