Clams will stay alive at least a week as long as they are cool and damp. I used to dig commercially for crab bait in Alaska when I lived in Kodiak. We ran across Shelikof Straits to Kukak Bay on the Alaska Peninsula and dug for 4 days and all we did to care for them was layer ice them. Then a day's trip back across to Kodiak, and deliver them on the 6th day. The oldest clams would be in as good of shape as the newest when we delivered. The coldness of the ice would put them into a state that was sort of like hibernation. As soon as they came out of the ice and warmed up they would get lively again.
Here at home, we regularly put them in the frig when we get home with just a damp cloth over them and keep them for three or 4 days until we clean them, if we are digging multiple days. That way we only have one mess to clean up after the clams are cleaned.
We never soak them after we rinse them on the beach, especially in fresh water, unless we're getting ready to clean them. If you leave them too long, they will die and fresh water hastens them dying.