The guy that had the truck before me used the center chain hanger for 5/16" chain. I took all of them off the truck as they were all rusted together anyhow. the center box is full of 1/2" chain and ratchet binders. The chain tray would be another 2" taller if I were to do this on my own. Several things that I would do differently if I were to set up a truck myself. Like a couple of pieces of pipe welded to the lower side under the box for the orange bar you see behind the box.
I second picking up all the mudflap you can. You'll never have enough of them. Every time I park I walk behind the trucks looking for the nice thick ones. Got any friends on the fire department? 4 inch fire hose is great for edge protection too.
I wouldn't buy anything until you have a truck. Just put that money in a safe place every week and don't touch it. What do you haul now? What do you think you'll haul?
If I were you, I'd start pricing boxes and racks. For myself, I prefer a good closed box with a chain rack in the center bay, side bays for miscellaneous equipment, and a tarp rack or box on top. That, plus saddle boxes, allow me to keep all my equipment on the tractor. Since I drop trailers at least once a week, and am the World's Laziest Flatbedder, I hate moving equipment from one trailer to the next. If you are also buying a trailer (not an option I'm looking at right now), definitely spec out a couple of tool boxes on the trailer as well. Never know when the extra storage space will come in handy, especially for tarps and short dunnage in winter.
Keep an eye out for stuff on Craigslist. I've bought alot of stuff for pennies on the dollar. Brand new never used tarps for $100.
It's like an auto mechanic. Start off with a small toolbox and wind up with a $25000 cabinet full that you need a rollback to move. Start with a truck and put 10000 lbs of headache rack and gear on.
Keep a grand in your hand. I bought my first headache rack (open) for $150. The next one was a 3 door that I bought for $300 at the TA in Baytown. Came with a a full set of lumber tarps. Chains, binder, straps, CBs...everything but bungees I've bought at a truckstop parkinglot. Especially if there's a casino nearby.