1) A coverup with sleeves
I picked up this dress on ASOS after seeing it on Girl With Curves and I love it. I can wear it off the shoulder like I am here or pull both sides up if I want full coverage. Regardless, my arms are covered (a great thing when I've had too much sun) and the swing shape plus white color keeps me cool. I've paired it with denim shorts because chub rub is real folks, even when you're at the pool.
2) A sun hat (the bigger the brim the better!)
I bought this hat a couple years ago I think and it's done wonders for my pool game. Whether I'm sitting on the side or in the water it shields my face and helps me spend more time outside.
3) A tote bag/cooler
I tend to feel pretty blah after too long at the pool (I'm more of a beach girl I think) but I've used this bag to bring lots of water and snacks with me whenever I go. Since it's a cooler not only does everything last longer, the random other stuff I throw in there tend to stay dry.
4) & 5) Sunscreen and Water
No matter how much I/we might love the sun, the sun does not love us. Please be safe and wear sunscreen whenever you go outside, but especially when you're planning to get some concentrated rays at the pool or the beach. And don't forget to reapply! I never understand why I don't see the people around me doing so and I have to resist the urge to scold them. And since you're also sweating plenty (whether you feel it or not), keep water and other liquids on hand to rehydrate.
Dress: ASOS (also available in Tall) ~ Bikini: Figleaves (old, similar) ~ Hat: Lou Lou Boutiques (old, but some similar options: one, two, and three) ~ Shorts: Forever21+ (old, similar) ~ Sandals: Ebay ~ Bag: ban.do ~ Sunglasses: Kate Spade