Tuna/Chicken Salad Extenders

While this isn't really Kosher a Kosher topic, it's a topic almost unique to NY style Deli's of old and doesn't seem to fit anywhere else on this board. I spent some years working foodservice for some former open air NY sandwich shop owners that retired down south. While I learned some marvelous tricks of the trade that made NY Deli style salads and sides unique and rarely discussed or ever seen in print in any Deli cookbook, I never had the opportunity to learn how to use extenders such as bread,crumbs, and other extenders that were common in NY and old time Deli's. While I'm privy to many of the secrets that made the salads special, this is one area that we never did, but was made aware of. Can anyone provide any insight to the use of extenders?