The RSVP Card enclosure

Even though they're not required, hosts have been providing reply cards in self-defense for so long that now most guests expect them -- with stamps, even. If you decide to use one, you can choose a separate card with self-addressed envelope, or a postcard. Give them a deadline, and a place to write their names and whether they're coming. (Smart tip: Since people sometimes forget to write their names on the reply card, number your guest list, and then lightly pencil the proper number on the back of each reply card before tucking it into the addressed invitation.)