I realize this discussion is about Littlenecks and Manilas for steaming, but if you are getting some two to three inch Butter clams during your digging, one of my favorite ways to cook them is to split them in half with a knife and coat the clam half with a dusting of seasoned flour, then cook the half shelf clams in a frying pan just enough to brown the flour coating.
Place the clam with the flour coated side down.

You can also cook them in a deep fat fryer. It actually works better since the hot oil cooks from both sides , they are quite tender.

Do not overcook them as they will get tough if you do so.

I have frozen clams that I have sliced in half and they have always been fine a month or two later.

Steamers never last that long around our house. If we don't finish them off the day we cook them, the cooked clams get plucked from the shell and go into a salad or pasta dish the next day.