Here are a number of phrases used when saying goodbye to friends or family as the 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 British English)
Did you enjoy your time in (destination)
How was your journey / flight / trip?

By Kenneth Beare, About.com Guide

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