It is a common expression, but is also a joke. This is what you would say when you are putting food out for pets or animals. Or if you are feeding a group of Cowboys in the 1800s. We do say this. If I cook a big meal for my family, when the food is ready I might walk out of the kitchen and say "Come and get it!" It is humorous and informal.

"Come and get it" is an imperative statement requesting someone to eat. The context clue that helps you come up with this interpretation is the first sentence.

come to the table and let's begin to eat.