What are some good things to have in a first aid kit for burns and sun burns? is capsaisepine a good thing to have, since it blocks heat receptors?

No capsaicin is: Not a good thing. An Aloe cream and a spray made for sunburn to take away the pain. Some have lidocaine . For burns some bacitracin and telfa and gauze wrap and paper tape .

Prevention is #1: Always start with sunscreen, but if you do get a sunburn, gels that evaporate and cool the skin feel the best, like aloe Vera gel. For other burns, always cool the skin as quickly as possible. The instant cold packs work great for this. Topical sprays with benzocaine help the pain, ie Solarcaine. Antibiotic cream, nonstick pads instead of gauze pads and tape. I would not use capsaicin .

Minor burns: Capsaicin cream is specifically contraindicated in irritated, damaged or broken skin. I think a burn qualifies as that. For minor burns which is all you should be treating yourself, is cool cloths, and perhaps an aloe Vera lotion and perhaps .5% hydrocortisone cream. Tylenol (acetaminophen) and Ibuprofen for pain.