I can't say it's a total dealbreaker if I didn't...but really early on when you're talking to the one guy in Goodsprings an option comes up that says "Want to play Caravan?" or something to that effect. So of course, my boneheaded self didn't proceed down that line of dialogue and now I can't play!

Do I have to start a new game, or can I build a deck through other means to be able to play?

The guy was Ringo......I thought the dialog option would come up again....no?

Mine did.

If you can't get him to build a deck, you'll have to make a new one. Just buy 8's, 10's, and Kings. No biggie.