I found a plastic storage basket at WalMart that's about 81/2 x 121/2", 5" deep (interdesign basket medium). One fits behind each front seat (adjusted all the way back) & is handy for all the whatnot.

My rear storage box design prolly wouldn't be so good, as it's not flat & incorporates an amp, sub, scuba tank & enough tools to do anything short of an engine rebuild.

And yes, I've been known to drag way too much stuff around with me.