What creams/oils can I buy to treat skin cancers? Do chemical peels kill cancer cells before they multiply?

See a doctor. Over the counter creams and oils do not treat skin cancer. Be sure to see your doctor to be sure your treated appropriately. Sun block is essential to help prevent skin cancer.
None. There are topical agents that you can use to reduce your risk of skin cancer...Broad spectrum sunscreen, retin-a, anti-oxidant creams and serums, immunomodulators, etc. Peels and lasers can also reduce the risk of developing skin cancers in at risk populations. If you already have skin cancer, you should see a skin specialist. Don't try to treat these yourself.