Situational worship is a form of worshiping a god to advance a certain situation. Examples include saying quick prayers to Danu while learning magic. Sacrificing books or wooden tools to Uastra before straying from a forest path. Asking for Gataurs blessing before climbing anything higher than a hill. Praying extensively and exclusively to Januri while at sea.
All gods have a wide and varied range of things in their portfolio and the ceremonies, customs, superstitions and rituals performed during situational worship are thus also very varied and frequently different from region to region, race to race.
Most priests don't believe the gods or any divine servants nearby actually base allot of their actions on this form of "petty, opportunist, worship". But it rarely hurts to try and appease the host before entering it's domain.