Bringing my iPhone to the beach, how to keep it safe?

This will my first time going to the beach since I got my iPhone 4S. I'm concerned about the possibilities of water damage. I would prefer not to bring it, but I really want to take pictures of the beach, especially now that my phone has a higher quality camera. (And I'm not bringing my regular camera, I'm better at taking pictures with my phone for some reason) I also want to take a quick video, and then simply just in case of emergency. I was considering purchasing a waterproof case, but the cheap but durable ones I found online wouldn't arrive until Tuesday (with one day shipping), and that's the day I'm leaving. These cases aren't at my local stores, and I don't want to invest in anything expensive since I'd only be using this about once a year. What are some ways I can protect my phone on the beach?

I'm also concerned about theft. I will be with about 6 or 7 other people at the beach, but they'll be around the shore/ocean and our items will be unattended. Last year I brought my phone because it was one that most people wouldn't find valuable, but I'm definitely more concerned about bringing my iPhone. How do I make sure to keep it safe, even when out of range?

I would suggest either putting up the money for a cheap photo/video camera specifically meant for harsh environments. If you're set on the iphone, a plastic ziplock bag might keep it safe, only pulling it out when you plan to use it. I hope somebody else has some better suggestions, that's all I've got.

I usually Take! Mine in a plastic bag and bury it in the sand.