A retirement party is a big milestone, but the timing is tight. You have exactly two weeks to pull this together before you walk out the door for good.
Focus on the guest list and the menu first. You want to lock in the pizza order early so you aren't scrambling while you're trying to pack up your desk.
Remember that the 0% intro window is a deadline, not a gift. If you haven't paid off the $300 by the end of the 18 months, the bank will start charging interest on whatever is left.