What should I do with extra pain killers from surgery?

It Depends. If you keep them, be sure to lock them up. Don't just leave them in your medicine cabinent where visitors, kids, cleaning people can get ahold of them. Don't flush them down the toliet which just pollutes the water supply. If you discard them in the solid waste stream (garbage), make them undesirable by putting them with coffee grounds, kitty litter, etc.
Collecting points . Depends on your local authorities guidelines. Most commonly unused drugs are collected at the designated police stations or pharmacies. Thank you for taking steps for not letting drugs to get to wrong hands.