I built a temporary " egg crate" for my BGE out of 2x4's using a drill, and a handsaw.
The pics are from when I just finished it and since then I have added the essentials i.e. a paper towel roll holder, a bottle opener, and hooks for tools. I added a row of hooks along the back top rail (hinge side) that holds all kinds of things - mapp torch, small bellows, ash tool, bbq glove, etc. There is space to keep a few chinks of wood, fire starters and other odds and ends in a not very organized manner, but at least they are close at hand.
Since then I have thought about building another rolling crate, whcih could be rolled up to any one of my cookers, with a works surface on top and storage on a second shelf (since the egg wouldn't be in it). I find this really functional, better than the nest sold by BGE, since it doesn't have the potential to tip over (besides having some storage space. The footprint is about 2'x2'.