The OP mentioned snorkel gear (as opposed to scuba gear). Even in the case of the latter, I'm personally okay with using loaner equipment that is supplied by nearly all dive operators. Wet/dry suits might be an exception (i.e. think genital contact), but I only dive in warm water myself. Additionally, some people like to bring their own masks, especially if they have prescription lenses; masks are easy to bring with you. But, flippers, snorkels? Come on!