Steamer clams can be kept alive in a bowl covered with a damp towel in the refridgerator for about two days, in fact more. If you bring some seawater home in a large plastic bucket, and can place it in a refer, and have access to an air compressor, you can place the clams in the bucket and bubble some air into the bottom of it, you can (lively them up) for a few hours at which point you could resume the process. Try not to shock the clams by putting them into water too much colder than the the clams are when you immerce them in it. I have kept both clams and oysters for over a week this way.