Since they've sailed out of Galveston, it's been when we first see the ship while getting Starbucks across from the harbor. On our Port Canaveral based cruises, once we got on the Disney cruise shuttles at MCO. Although putting our luggage tags on the night before we leave the house (last thing before we load the luggage into the car) also is a big trip moment for us. Boarding and looking up in the atrium makes me cry. Hearing the horn is pretty awesome but I'm all the way into vacation mode by then.