I have my Garmin 2720 on the left side of the shelf on a Stem Stand so I can reposition it, and a radar detector on the right side inside a plexi-glass garage I made to keep most of the rain off of it.
In the middle is an AmpliRider mixer. I also have the volume control for the AmpliRider on the far right side and a small box with a pair of ground isolators on the far left. The isolators don't really need to be on the shelf, and AmpliRider now offers the mixer with volume control on the mixer itself rather than a separate box, so these are not necessary.
I also have a FRS/GMRS radio on the left handlebar and a SPOT tracker on the right handlebar. It is pretty busy, but I can't think if anything there that I don't use all the time except for the two-way radio.