Following Holy Communion, we should avoid spitting or chewing gum throughout that day. This avoids the sacrilege of spitting out the Holy Mysteries, as well as avoiding scandalizing other people. Hold off on brushing teeth until the evening.
Just as we fast for about nine hours prior to Communion, so too there should be a "joyful fast" from worldly cares after Holy Communion, if possible: quietness, prayerful reading, family time in activities of a gentle spirit.