Small set of whetstones so I can keep my kitchen knives absurdly sharp. Sharp vs "meh" vs dull knives make a huge difference in speed, comfort and safety. I've scuffed my knives a bit getting into things, but at least they're sharp as hell and touching them up only takes a few minutes.
Also it's hardly unconventional, but a quick read thermometer (fold-out type) is almost a must.
All you need is a bulldozer and a cement truck.