Cut a bottle down to get a flat sheet of plastic. That makes a nice flexible shim to open low-security doors. Plenty of other uses for the plastic - cutting board, knife sheath, etc. The bottom of a bottle makes a decent, but small, bowl.

With something like yeast and sugar to generate CO2, you can make mosquito traps out of the bottles. Not terribly effective, but interesting.

I've seen a diagram for an improvised water trap suction system for pneumothorax. Quite involved, but possible.

You could maybe use one (or several) as the pressure vessel for a hydraulic ram pump to lift water.