While mine is a homemade bumper, it is along the same design as the Aluminess. I keep a floor jack, POL, recovery gear, flares, coveralls, and some other maintenance gear. I am tacking on a few round stock along the top to hold water a fuel jugs as well.
Front has Warn Winch, winch extension, and a full set of lynx levelers. I could probably get the snatch block in there too. I keep the winch control inside the van with a tree saver, pair of soft shackles and a kinetic recovery rope.
Rear is currently empty but I'm planning on storing a second set of lynx levelers (not sure they fit) and fluids (great idea loren85022). It'll have other assorted bits like air hoses and such but I want to leave some room for muddy clothes to have a temporary place to cram them without dragging mud through the van.
Store two sets of Camco leveling blocks up front. Blocks are in two Sea to Summit tapered dry bags. The dry bags keep the blocks from holding water and from bouncing around. Rear is typically misc tool/recovery gear storage. Use dry bags with the gear in the rear as well. Cut tool chest style anti-slip liner to fit both bumpers (another attempt to keep slippage to a minimum). The liner is perforated and won't retain water. Easy to pull out and rinse off if necessary.