Some random thoughts on this topic:

"Shell": I was using a self-designed keyboard shell at one time that was essentially three pieces, a large flat back and two sides, hinged with removable shelves. The idea was that the keyboard stand would look sort of like a Hammond B3 when in use, with the sides folding in and locking when the shelves were removed. I also had cord managers and a power strip inside of it so no cords were visible from the audience's perspective. It held two 76-note keyboards and it worked and looked great. The guys who did the carpentry work actually started making them en masse and selling them for churches and home use (but no longer do). And a rock band saw my stand and designed something similar for themselves in flat black. Still it was more work than I cared to go to and required a van to transport: it was heavy and I was always scared of scratching it up.

Also more recently I was using a wheeled QuickLok "Z" stand with a mixer/EQ and all of the power supplies/cords etc. mounted to it. I rolled it fully assembled in and out of a van. This worked and was quick setup but it was very heavy. I parked the beast in my studio.
I now use a Quik-Lok Monolith stand with no setup time.

MP3/CD player: I use a Creative Labs Nomad with a 20GB hard drive - plenty enough storage for thousands of files so I never need CD's. I also use it occasionally for recording my gigs live (yep it's a recorder too). Very handy.

Amp: I still have a full JBL EON-based PA if/when called for but mostly I use my Motion Sound KP-200s for everything. One piece complete stereo amplification system.

Current system: Yamaha 9000 Pro, Monolith Stand w/bench, KP-200s amp, Nomad. Setup/takedown time is about ten minutes and it all fits easily in a VW Cabrio.