What are the essential "must-have" tools for the beach?

Panama Jack Polarized. Usually around ten bucks, they never break. My Oakleys break, these don't, figures.

Sandal/flip flop Anything with leather/fabric will take a long time to dry. I have a pair of $9 old navy flip flops that serve me well at beaches, pools, and short walks. They're cheap, all rubber/plastic (dry quickly, clean easily). They're not good for long walks but are perfect for ro om/car to beach/pool. I've always considered the Reef Fanning line for the in-sole bottle opener but I can never justify the price (plus there are so many ways to open a bottle that are cleaner than the bottom of my flip flop!)

There are definitely better flops and sandals around; I'll be following this thread.

Sun hat

I highly recommend a sun hat of some sort.

I currently have a cheap and cheerful hat I bought from Amazon UK, but pretty much anything that keeps the sun off your face will help to keep you cool, while also reducing the appearance of aging and the probability of skin cancer.

Also keeps rain off if the weather takes a sudden turn for the worse (I did mention that I live in the UK, right?) ;)

Not in your requested categories, but I find a good shovel to be indispensable for both setting up on the beach and also for playing on the beach. We use a great compact shovel, the Cold Steel Special Forces Shovel and have made the day of many kids who have run up and begged to borrow it. The edges have very slightly rusted after years of beach use but it would probably wipe off if we were worried about it. The only potential concern is that the edges are pretty sharp, you have to make sure kids respect this shovel and don't thwack siblings with it. :)

Every single thing that is required while going to beach or in water is important. So make a list of it and don’t forget to grab all the stuff. To enjoy the underwater scene I would recommend you to go with swimming goggles from contact lens heaven, which would be protecting your eyes from infections as well will be giving you the clear view to enjoy everything beneath the water.