I paried the package with a navy envelope andd matching envelope liner. The navy envelope had white ink printed for the mailing address. An alternative cheaper option would have been to design a really nice/unconventional mailing label that would wrap around the top of the envelope.
The invitation card
They wanted an nice, but not too formal wedding invitation. She had expressed that her overall feeling for the wedding was "fun.. more like a party, rather than a formal day." She had mentioned some lace, or twine to wrao around the invite for extra swag.
The RSVP card
Like many of my clients, they don't want to spend a fortune on their invitations. This is one (of many) perk to hiring a graphic designer to do your projects. It's one of our jobs to not only design something beautiful, but do it within the financial specifications. One easy way to avoid an un needed cost, is to have your RSVP be a post card, instead of a card within an envelope (you're removing the cost of the extra envelope purchase/printing).