Line plant pots. When repotting your houseplants, cover the drainage hole with a coffee filter before adding the soil. Water can easily drain away when you water your plants, but the filter prevents soil from leaking from the bottom of the pot.
Drill a hole in the side of the bottle near the bottom and feed your lights in through the hole. Plug it in and you've got yourself a rather novel little bit of mood lighting. Add colored or clear stones/gems.