On the Saturday before Independence Day, my family always hosts a Fourth of July celebration. There is usually a water balloon fight, lots of beer, an awesome display of fireworks, and a wonderful variety of food. There is always something catered, like chicken, and lots of different sandwiches, potato salads, sushi, etc. Once, we hired a pig roaster. It was fun, but the expense was too much. Last year was the best Fourth of July party so far, because we decided to have a clambake celebration.
I would suggest going the seafood route to anyone contemplating throwing the sort of summer celebration that we normally do. True, it is never actually "cheap" to hire professional catering for a party. But, if you are already set with decision of catering the event, the seafood route isn't much more expensive than the usual chicken, potato salad, macaroni, etc, that caterers typically offer.
A couple hundred people often show up for our Independence day celebrations. Not all of the people show up at the same time, but they come and go over the course of the party, and I guess that 200 or more show up every year. For a successful clambake celebration, you ought to have at least 40 people show up. If you don't have that many people, you may find that you end up having too much stuff and not enough participants. When there are enough participants, it would be worthwhile to have a clambake celebration.
Of course we offered our clambake party through a catering company. We ordered a complete menu, which included mussels, clams, lobsters and quahogs. The bought over the live lobsters and cooked them in place. Part of the fun (both for adults and children) is to look at the chefs doing this. They also lay out lots of rocks and seafood and they they serve the food on top of it.
What we ordered was considered to be a "standard clambake" but they also had an option for a "New England clambake". Both were similarly priced, but I guess that the New England one had more local menu offerings for New England stuff. I was pleased with the one we ordered, but I cannot say anything about the New England style, because I haven't tried it (yet!)
Last year's 4th of July clambake celebration was so wildly popular that we couldn't dream of changing the food this year! This year's party is already fully planned, including the fireworks, water balloon fight, and beer that everyone enjoyed last year, and we can't wait for July to come!