Put yourself in your guests shoes when considering their experience. If you're bringing them to a warm and/or humid destination from a cold location, do what you can to keep them comfortable. This means offering (welcome bags & hospitality baskets) and suggesting things that will keep them safe and feeling good:
Bottled water, sunscreen, skin moisturizer, off wipes, chapstick, ibuprofen packs, mints, flip flops, and most importantly a guest guide for the weekend.
The bag above is one of the best I've ever come across. It's large enough to carry items down to the beach and pool, but small enough to pack away in an overstuffed suitcase. And at under $6 each...A STEAL. And the cute bags below- I love these for bridesmaids gifts. Perhaps with a nice thank you note inside along with lip gloss, a mirror, and blotters (to fight the mid-reception shine).