When your aunt's BFF comes with a husband and three children, these additions to the headcount mean more mouths to feed, more chairs to sit in, more wine to sip, more cars to park, more silverware to eat with and more glasses to drink out of. Because you don't want to hurt any feelings, the body count can add up quickly. And because many of these expenses are on a per-head basis, the tab is going to reflect that. Get a number in your head, and work backward from there. If that second cousin twice removed needs to go, then so be it.