What a fun theme! I like the idea of the pail and shovel instead of bags. A friend of mine had a pirate party for her DS when he turned 5 and she had a pool filled with sand and treasures. It was a big hit with the kids. I would make sure that someone is watching the children if they are all going to be Nolan's age or toddlers, because you don't want them to accidentally eat the sand or one of the treasures! :)
Do you have a Party City in your area? I have found that they have a lot of great supplies, and as you go in the front of the store, they have a display stand with flyers printed with party ideas for different themes (luau, fiesta, over the hill, etc) and they give you party supplies needed for that theme.
Also, go to the library and check out some books on parties for children. I did this and it was really helpful! I found a lot of ideas for beach party themes in some of the books. DD had a Little Mermaid party for her 4th birthday. I had set up an area where they could run through a flamingo sprinkler, a kiddie pool to splash in, a ball toss game, and then we had our playset as well. I served pizza and had cake. For drinks, I filled cooler with ice and had bottled water and juice boxes (apple, grape, and orange).