One more expansion/clarification on an earlier post: have both an enclosed oil drain pan (the kind that has a drain and storage volume with a cap), as well as a conventional open pan (although you can use the top part of the enclosed drain pan as well). The open pan is for draining when you want to check out the parts coming out of the pan or rearend. In my case I was retrieving my distributor cap screw that had fallen in, and also checking the roller lifter parts, trying to do a post-mortem to figure out which part failed first. The enclosed pan is nice for transporting the drained oil to the track's oil dump tank, or home if the track does not have one.
I am planning to make a bunch of racks for the walls of my trailer, to hold lightweight but bulky items (like the aforementioned drain pans) up near the roof and out of the way.
A couple other plans - running 12V landscape lighting, with inside and outside mounts and plugs so that I can move the lights outside. They have some pretty bright ones available as well as LED bulbs that are almost as bright at a fraction of the wattage. Also planning to add a heavy-current circuit to an accessory socket (cigarette lighter) near the back of the trailer, both for using 12V devices (like a small air compressor for topping off the slicks without getting out the big compressor), and for topping off the battery charge on the drive to the track. Currently working on wiring in a bunch of AC outlets inside and outside the trailer, getting tired of always tripping over extension cords!
Not sure if it has been mentioned yet, but a broom and dustpan also come in handy!