Abandon ship! At least you aren't actively sinking, and if it really is a gas leak, it makes it's own signal flare.

Grab the least amount of stuff you NEED, grab stuff that floats and is/or can be made watertight. Agree on a meeting point, and stay together. And hope everyone can swim, becuase if you really do have a gas leak, you don't have time to build a raft out empty cooler bottles and a lightweight conference table.

Now, if you'd said a gas leak AND a fire, I'd probably answer "try not to die".