Final answer:
Informing a friend or family member of your itinerary is the most important action before any trip.
Step-by-step explanation:
The most important action to take prior to any trip, regardless of length, is to inform a friend or family member of your itinerary. This ensures that someone is aware of your plans and can alert authorities in case of any emergencies. It is a critical safety step and surpasses other actions such as packing, checking the weather, or travel documents in terms of immediate importance for traveler safety.