You guys have covered a lot of it...
Lifting tools are the best. Cherry Picker, long lifting/pry bars, furniture dollies, etc. Come-alongs and small jacks are great for positioning, like pulling an axle into place.
Anything to make it easier on the body. Kneeling mats, knee pads, rolling stools, shop chairs, good creepers, etc.
PPE for sure. Find ear plugs that fit well and buy a shitload of them, and muffs for louder work. I seem to tear up my hands so I wear gloves all the time - either nitrile, or cut resistant dipped, or leather. The basic 3M respirators with replaceable filters are good enough for most uses. I wear glasses so DeWalt over-the-glasses safety goggles are awesome. Invest in legit fall protection gear, it's worth it.
BUY GOOD LADDERS. Enough said.
The best purchase ever - pallet forks for my tractor. If I had unlimited space and budget I'd own a forklift (and a skid steer, and a mini-ex, and...) but since I don't I'll use my jack-of-all-trades tractor.