When purchasing party supplies, keep in mind that guests take a new napkin, cup, plate, etc. every time they go back for more food and drink. The longer your party lasts, the more supplies you'll need.
When calculating the number of appetizers or hors d'oevuvres to provide, keep in mind that guests don't usually eat much until after the first or second drink. That means the first hours will be more drinking than eating.
When deciding what drinks to provide, keep in mind that high-end bourbon (Maker's Mark) and vodka (Grey Goose) are increasingly popular.
When buying anything, keep in mind that it's better to have too much than to run out. KEEP YOUR RECEIPTS and you can return unused non-perishables (paper products and unopened beverages).
When planning your event, consider a theme party ("red and black," 1960s, Sex and the City). They are fun and easy on your budget.