Use them to make robots. The containers can be their bodies(you could turn them upside down to have a body that is smaller at the top), and you can cut another one for the head, and experiment with making legs or wheels or whatever robot-mobility acoutrement you like. paint them silver or bright safety yellow with black stripes and glue on assorted electrical bits and bobs, or paint details on them. Make a secret compartment for hiding stuff.
lockwashers are designed to bite into the surface of the item to which they are(with a screw or bolt and enoguh torque) attached, effectively locking the hardware in place. keeps the hardware from vibrating loose. Just so's ya know
spacefruit jewelry--so super cool! Me likey. I too have considered making stuff out of old shampoo/conditioner bottles. Does anybody have any ideas on getting the printed stuff off the bottles?? Thanks, K