THE TRAVEL COMPANION
Without the built-in vacation buddy of a romantic partner, you're still going to want to share this fun: the planning, the pictures, the avoiding the rip-off of "based on double-occupancy" fine print.
THE EMERGENCY CONTACT
Is this your roommate? Work husband? Or even your closest sib (geographically-speaking). When trouble comes a knockin', who you gonna call?
THE ACCOUNTANT
Part of coupledom is having built in checks and balances. Flying solo means it's that much easier to let aspects of grown-up life get out of whack. Getting your financials in order? Keeping up with preventative maintenance on your car, your pets, yourself? This friend knows what time it is. While the title may be metaphorical, the encouragement to focus on the big plans is real.
THE WEDDING DATE
Also known as The +1, The Seat Filler or The Is That Your...? Afraid you'll get seated at the kids table at Thanksgiving, because everyone else is coupled off and they want an even number? Charming, amiable, energetic dancer? This is the friend to call.
THE CONFIDANT
A best friend, a soul-sister, your brother from another mother. Whatever you call this friend, they'll be there. In fact, WHENEVER you call this friend, they'll be there. Whether you've known each other since childhood or it just feels that way, you know the bond you have can't be broken by physical distance, a genuine political disagreement or even a session of really ugly crying.
BONUS: THE AIRPORT PICK-UP FRIEND. If this isn't an alter-ego of one of the friends above, well, just find one. There's really nothing better than being greeted at the airport by someone who can spell your name correctly on a cheesy sign.