Is there anyway I can surf while on vac in maui if I have a sore and I am on bactrim (sulfamethoxazole and trimethoprim)? Can I bandage the site -elbow- enough to reduce exposure?

Infection. Without knowing what you mean by a "sore" and what is causing it, this is very speculative, but if you are being treated for MRSA with oral Bactrim (sulfamethoxazole and trimethoprim) you should be fine. If this is topical you can reapply it after surfing. Or you could try and find a waterproof occulsive dressing.