Beergraphs has a good primer on how to think about grabbing the stuff that goes quick.

If they’ve got a great selection, there’s a chance that the really great selection is chilling in the cooler out of sight.

This is very good advice.  If you’re looking for something–just ask.   But beware…

It’s not sufficient to go to the clerk and ask to see a list of what they have in the cooler in the back. You’ll get a newby eye-roll and probably get no answer.

The whole thing is worth a read–especially if you’re new to craft beer and want to get in on the rarer and more infrequently distributed goodies.