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.
How to Light a Pumpkin ~ To illuminate a carved pumpkin... Wrap a strand of 20 lights around a glass jar, and secure wires with tape. Cut a hole in the hollowed-out pumpkin for the cord, and place jar inside