How Was Venom Alive?

Venom sacrificed himself to protect his human host from Drake's exploding rocket ship, sending Eddie safely into the San Francisco Bay. The closing moments reveal that Venom survived the blast and is once again bonded with Eddie.

How did Venom survive burning?

In the comics, Symbiotes have been known to survive and regenerate even if only one small part of their mass survives. So, when Venom split into multiple pieces that apparently burnt up during the finale, arguably one of these pieces could have survived and latched back onto Eddie as he fell into the water.

How did Venom survive rocket blast?

Venom was able to survive the explosion and the fire because he could heal himself. He may have been burned and believed he would die, but he was mistaken. Venom only feeds on Eddie's organs when he doesn't get the food he needs (i.e., living things).