If you were in S.A. I could help you, I go diving alot so I know where most of the shops are, but If your just going to go snorkelling you might just get some stuff from academy and that would work fine. However, what I found has worked well is (depending on where you go) to simply get the stuff there. If its like a resort town e.x. key west, etc. or something they will usuallly have a better selection than any place here would. Sometimes, they will even have better prices because they have more competetion. Where are you going snorkelling anyways?
If anything just cannot go wrong, it will anyway.