外出时告别

Goodbye. Have a nice trip.=Goodbye. Hope you have a nice trip.=Bye. Enjoy your trip.
再见，旅途愉快。
A: Goodbye. Have a nice trip.
再见，旅途愉快。
B: Thank you. I'm sure I will.
谢谢你，我一定会的。

Goodbye. Have a nice flight.=Goodbye. Hope you have a nice flight.=Bye. Have a pleasant flight.
再见，一路顺风。（用于机场告别）
A: Goodbye. Have a nice flight.
再见，一路顺风。
B: Thanks. See you in a few weeks.
谢谢你，过几周见。
flight n. 飞行，航班

I'm looking forward to seeing you again.=Looking forward to seeing you again.
盼望能再见到您。
A: See you when I get back.
我回来以后再碰面。
B: I'm looking forward to seeing you again
盼望能再见到您。
look forward to中的to是介词，所以后面如果接动词的话要用ing形式。

Good luck.=All the best.
祝你好运。
Good luck with your family.
祝你全家好运。
Goodbye then, and all the very best.
再见，祝你一切都好。
A：Good luck.
祝你好运。
B：Thanks．
谢谢。

Be sure to drop us a line=Remember to drop us a line.
别忘了来封信。
Remember to give us a ring
别忘了给我们打电话。
Don't forget to send me a message.
别忘了给我发短信。
drop sb.a line“写信给某人”

Take care．
多保重。
A：Take care.
多保重。
B：Sure．Bye-bye．
我会的，再见。