We typically bring a soft sided cooler with meats etc. One time we were told it's $20 fee, others we've been waived thru.

It has less to do with saving money or finding the right quality than it does with wanting items essentially prepared in advance to save effort on the boat. We also stash a sharp ceramic knife in there because we rarely find a good sharp knife on a charter. It's a bit of a pain to check the bag but it's been worth it. Without that we'd show up with lightly packed duffels and wouldn't check a bag.

Preformed and seasoned burgers
marinated chicken
pre-cooked bacon
steaks cut to serving size
shrimp and/or scallops sometimes