Cabinet Hidey-Hole - Between almost every pair of upper cabinets, there's a 1/2-in. gap. Take advantage of that gap by hanging a manila envelope containing, oh, I don't know, about two grand in hundred-dollar bills? Hang the cash with binder clips that are too wide to fall through the crack.
Hide a Key In Plain Sight - Say you want to hide a key—other than under the rug or over the door. How about mounting a phony plastic LB fitting? Screw it to the wall and run a bit of 1/2-in. conduit to the ground so it looks official. Cut the head off the bottom screw and glue it in place. That's it. Swing the cover aside and there’s the key.