You are looking at twenty family members sitting around a table, and somebody has to feed them. Graduation season gets booked up fast, so the real lever here is timing rather than last-minute scrambling.
Start locking down caterers about three months before the crowds hit. Getting your dates on the calendar early keeps your options open and stops you from paying rush rates.
That 0% intro APR for 15 months on purchases and balance transfers is a deadline, not free money. If you still have a balance left when those 15 months run out, interest kicks in on what you owe.