Ours included the invitation card, an outer envelope for everything inside, an info card with various info on it (website to RSVP at, hotel info), an RSVP card,

Ours included the invitation card, an outer envelope for everything inside, an info card with various info on it (website to RSVP at, hotel info), an RSVP card, and an envelope for the RSVP card. I'm 99% sure we attached stamps to the inner envelope, too. We bought the envelopes, but made the cards ourselves to make them more personal and cheaper. (We had a paper cutter and made detailed cutouts in the invite.)