i was taking my hard top off and noticed,(which i dont know why i never wondered what was behind door #1) behind the driver side seat is a panel. i took off the screws and theres a bottle behind it with hose's going to it. i own a 72 bronco. what in the world is this bottle for any one know???

It captures fuel vapors from the tanks and allows lets any liguid fuel go back to the main tank. From there the vapors are sent to the charcoal canister behind the front passenger side wheel. Those fumes eventually get sucked into the air cleaner and burned in the engine.

ok, could i plug the lines, do i need them?

You could plug the lines and get rid of the tank and charcoal canister but then you would need to use vented gas caps. It's really a good system to keep in place. It keeps your garage from smelling like gas.