I am a surgeon so not infectious disease specialist.
Yes, a negative test indicates you very likely were negative on that day. (PCR is not 100% accurate).
So in addition to negative testing, you need to "follow the rules" (Isolation, mask, face shield, hand hygiene) PROPERLY, which means mask covers mouth AND nose, I personally will wear N95 mask in high risk areas(on the plane and other crowded areas). Also if feeling bad, self isolate (which may mean not taking flight you are suppose to take in a few hours).... Mentaly, this is hard to do.
This needs to be ongoing weeks before trip and continue on the trip.
Outside, away from others, remove mask. Luckily I will be on boat,

Doing everything right, and you still have a risk of virus. Not doing EVERYTHING as you will greatly increase your risk of infection (and thus increase risk of others.