You're standing in a store for party supplies with a trolley half full of balloons, a backdrop and themed cups, and you're still not sure what guests will do for two hours. That's the gap most budgets miss. Decor might make the photos, but it won't fill the time between arrival and cake. Treat this as one budget decision, not two separate shopping trips. Decide what to buy, what to rent, and who'll do the setup, storage and weather backup…