Invite: Send a coded message via covert means. (This invitation will self-destruct in three...two...)
Décor: Plaid, crests, swords, and cut-out letters
Movies & TV Shows: Alias, the Bourne movies, and Buffy the Vampire Slayer
Craft: Make a hair bow out of coordinating plaids; create a super secret book cover to hide your covert texts; hollow out an old lipstick tube or some other innocuous-looking container to form a secret carrying device; make a holder for all that dangerous/killer spaghetti.