Have a good trip! And definitely, "see you next time," rather than "farewell!"

(I heard that definition of sayounara before myself, but I've discovered that it's not quite accurate, as the teachers at my school say "sayounara" to me as I leave every day. Basically, as I understand it, sayounara implies that the next time you meet you will have "turned a page in your life." So, if you think you're turning pages every day, you can say sayounara every day, but most people don't see their lives that way. Anyway, there's some trivia for when you come back to Japan. ^_~