I've checked a cooler on board twice. Both times it contained lobsters, those ice packs, some salt water, newspaper, and sea weed. Both times this was done at PWM, where they probably see this happen several times a day.

BTW, I've had a 90% survival rate of the lobster on these trips and they are going from PWM to SFO, so it's about as far in the 48 states from PWM as possible.