Calvin, I had a similar(ish) situation with TDF tickets once. I almost always bring my printed confirmation out with me to the box office, but one time I forgot to. Of course, this was also the one time my reservation happened to be lost. Luckily, it was a show at a smaller Off-Broadway company (Transport Group, maybe), and the box office attendant let me come back there and use the house computer to access my TDF account and show him my confirmation voucher.
I've never left the house without my confirmation voucher since.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body