The most important thing to have is all the safety gear needed for hands, eyes, feet and ears. Sometimes you may even need a hard hat to keep the knots off your noggin. After that is my air compressor because I have so many air tools and of course the ever present 4.5" grinders. I just finished making a little stand that folds up and down and supports my landscape rake when I unhook it. I used all scrap pieces and ended up using a battery powered Drill, 1/2" drill bit to enlarge and existing hole for the pin that locks the drop bar in place, 4.5" grinder to smooth up some edges on scrap, bench grinder to buff off some paint, welding machine, (18" pipe wrench and 12" crescent, 6" vise and an anvil to straighten out a piece of scrap flat bar and then bend it to my required shape)4# shop hammer to beat stuff to fit, channel lock pliers to handle hot metal. All this for a 15 minute job.
Nothing like having the tools needed when you need them unlike yesterday when down in the pasture and behind 3 locked gates and almost 1/4 mile to get to my shop when needing to do some field repairs to a dirt drag and all we had was a pair of fencing pliers and a 6" pipe wrench to remove some 1/4" and 3/8" nuts. Got it done but still later ended up going to the shop anyhow for some more bolts and heavy wire.