There are several things that aren't directly for the cattle that make life alot easier for me. I always carry a good pair of pliers, a couple of screwdrivers (flat and phillips), a 9/16" combination wrench (fit's our fans mounting bolts) and a ratchet with 9/16" and 5/8" (fit's our fan cage) sockets. A roll of electrical tape always comes in handy, too. I like to keep an old hand towel or two in addition to a roll of paper towels and a small bottle of hand sanitizer. You can use electrical tape and a piece of paper towel, but a few bandaids come in handy, too. These items don't take up much space, but they're sure nice to have when you need 'em.
David