I need it to be nice because i want to be able to go back there if i can
But, if you think that it'd be ok for you to leave without notice, just asking the manager or boss to speak to you in private, and then just let them know "I got a better offer for another job, and unfortunately I'm not going to be able to work here anymore." Telling them that you appreciate the time that you do work there makes you sound very greatful, and that tends to go a long way in getting re-hired if you do need it.