At a Pidyon HaBen I have observed that the Minhag is to put sugar cubes and garlic cloves on the tray with the baby. What is the source of this Minhag? And why specifically sugar and garlic?
According to this it's because garlic and sugar are spices which last along time and get put in multiple dishes. This way, people can take some of the garlic and sugar home and thereby be able to partake in the mitzvah-food for a long time to come. A similar idea can be found here.
According to this it's because sugar shows that mitzvot are sweet and garlic is a symbol for fertility.
People who attend a pidyon haben are counted as if they made 84 fasts, tanesim. Anyone who partakes of the feast of the pidyon, is likewise credited. Since garlic and sugar leave their taste in minute quantities, we cook and then distribute food with this garlic and sugar to be mezakeh many, many, other people as if they too fasted 84 fasts.