[Fiskadoro]

Put them in a 5 gallon bucket and put them in a fridge on a medium temp setting. They will last for days. What you do not want is ice cold water, a cold Ice pack or ice directly touching them as it chills them unevenly and they then die quickly. I have a little dorm fridge I use just for bugs and they will last days in a five gallon bucket. I've even had big lobsters rip of the legs of smaller ones and eat them after being in the fridge a few days.

After a day or two they will will slow down and eventually will hardly be moving but usually they are still not dead. With a dead lobster the tail will come loose from the back of the carapace leaving a gap, once you see that you should clean them immediately.

Some people think that a dead lobster injects some kind of toxin when it dies into the flesh. The truth is just like with fish bacteria in it's digestive track multiply after death but in a lobster it there is no gut to contain it and it can contaminate the meat. Colder they are when they die the less bacterial growth you get and the longer they last. In other words a lobster that dies in your truck, bait tank, or room temperature Ice chest is more suspect, then one that dies after a few days sitting in the fridge. If your worried about them spoiling cut off the tails and remove the digestive track, and then throw them on ice. Tails will last for days chilled or on ice, so if there's a question about them lasting clean them, chill them down, or even freeze the tails.

The big deal is if the meat is soft or mushy when cooked it's not worth eating. You want that meat to be firm after it's cooked.