Cockroaches are pretty hardy and are over 350 million years old, even predating some dinosaurs. The cockroach has a high resistance to radiation and is the creature most likely to survive a nuclear war.
They also do not have blood pressure like humans but rather, an open circulatory system. The pressure is so low that if you cut their heads off, their necks would seal simply from clotting. You may have heard that the body can survive without its head, but will eventually die only because it cannot eat. Surprisingly, the head can also survive for several hours waving its antennae. If refrigerated, it could last even longer.