Rod holders, Cup holders, a tray to put jigs/plastics on, Battery box, auger mount on sled. A personal favorite of mine is the frabill coat hangers. Never thought I needed them until I had one.
I took a 3/4" ninety degree pvc coupled and cut it so I had two equal sides. The I put a bolt attaching it to the sled on the back, because it was a ninety degree, it had some angle two it and I could swivel it.