Next on the fire would be the corn in its husk. Ten minutes later, add the lobsters, and cover with a light layer of seaweed. In another 10 minutes, add your steamers. You'll be able to eat the steamers in less then 10 minutes or whenever they pop open and then head into the lobster, corn and potato layers. The kids probably won't eat this, so you can wrap some hot dogs in aluminum foil and heat them with your steamers and give them an ear of corn.
Marshmallows are a good dessert idea.
The cleanup for your clambake is fairly easy. You can wait till the fire goes out, roast marshmallows and tell stories of how the Cape used to be, or cut to the chase and dowse the flames with a hose. Don't cover the hole for at least another 24 hours.