Abstract: A fuel tank plug structure has a cap assembly provided with a cap member and a push button combination lock, a fixing plate including a lever for cooperating with the push button combination lock, an intermediate portion below the fixing plate defining a interior storage compartment adapted to contain articles such as keys, money, etc., a clogging assembly provided with a tubular portion including a lower engaging portion configured to be removably, received on, so as to close, a container or vehicle fuel tank filler neck and a supporting member causing the intermediate portion to be engaged with the tubular portion through a sealing member. The push button combination lock has a slider which will engage the fixing plate with the intermediate portion upon depressing a correct series of buttons and will disengage the cap member from the intermediate portion when the correct series of buttons are not depressed.