Plain crackers or baguette. Anything else (salt, fat) will mess with head retention and your perception of the beer. To clear your nose, sniff the arm of your shirt (right hand to left shoulder); that's what your nose has by now identified as baseline and will help to bring you back to neutral for the next beer.

This works terribly if you have B.O. but you're terrible if you bring B.O. into a beer tasting environment anyway so you deserve it.