NB1& NB2: Saying goodbye

Here are a number of phrases used when saying goodbye to friends or family as they depart on trips, both short and long.

Long Trips, Vacations, etc. American English
Have a good trip.
Enjoy your vacation.
Have a good time in (destination)

Long Trips, Vacations, etc. British English
Have a good journey.
Enjoy your holidays.
Have a good time in (destination)

Short Outings
Enjoy! (American English)
Have a good time at (destination place such as a restaurant)
Have a good time in (destination city)

When your friends or family return home it is common to use one of the following phrases:
How was your vacation? (holiday in American English)
Did you enjoy your time in (destination)
How was your journey / flight / trip?