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Here's a few tips to keep in mind when packing for your next beach vacation:

1. Underwear - pack more underwear than needed; you never want to find yourself recycling a pair of dirty underwear
2. Bathing suits - always pack at least two different bathing suits; this way you can dry one while wearing one without worrying about it.
3. Clothing - the easiest solution for packing enough clothes is to pack one full outfit for every day you'll be on vacation.
4. Footwear - normally, the most appropriate footwear for the beach are flip flops, but it's a good idea to bring an extra pair of athletic or dress shoes.
5. Sun block - keep your skin safe with lots of sunscreen; my suggestion is 30 spf applied every couple hours depending on activity.
6. Sunglasses - pack your favorite pair of sunglasses or pick up a cheap pair before hitting the beach, this will keep you headache free and keep your eyes healthy.
7. Hydration - pack plenty of water to keep yourself hydrated, and make sure to pack a little Gatorade, Powerade or other sports drinks to put electrolytes back into your body.
8. Beach towels and chairs - if you're flying to your beach destination then I recommend waiting to get to the hotel to purchase or rent beach towels and/or chairs, however, if you're driving then I suggest bringing 'em with. 
9. Frisbees, bocce, and other beach activity - there's a million different ways to keep yourself occupied while at the beach, so make sure to pack a few games and supplies; I suggest packing water resistant games and activities.