A/C is not "resorty". When I describe San Pedro to people here I say "You can't tell the tourists from the locals. That's why I like it."
Do not buy new clothes for this trip. T-shirts and shorts are the order of the day and if they don't look new you will feel much more at home.
Shoes? Shoes? Who needs shoes?
Trust me -- pack light.

Harriette
Take only pictures leave only bubbles