There are a number of synonyms that can be used in place of the phrase "fill pockets". For example, the phrase can be replaced with "pad pockets", meaning to add extra filling or material to increase the size or thickness of a pocket. "Stuff pockets" could also be used to describe the act of filling pockets to the brim. A more playful phrase might be "load up the pockets", while a more formal option could be "stock the pockets". Other possibilities might include "cram pockets", "pack pockets", "heap pockets", and "pile into pockets". Ultimately, the choice of synonym will depend on the tone and context of the writing.