外出時告別

Goodbye. Have a nice trip.=Goodbye. Hope you have a nice trip.=Bye. Enjoy your trip.
再見，旅途愉快。
A: Goodbye. Have a nice trip.
再見，旅途愉快。
B: Thank you. I'm sure I will.
謝謝你，我一定會的。

Goodbye. Have a nice flight.=Goodbye. Hope you have a nice flight.=Bye. Have a pleasant flight.
再見，一路順風。（用于機場告別）
A: Goodbye. Have a nice flight.
再見，一路順風。
B: Thanks. See you in a few weeks.
謝謝你，過幾周見。
flight n. 飛行，航班

I'm looking forward to seeing you again.=Looking forward to seeing you again.
盼望能再見到您。
A: See you when I get back.
我回來以后再碰面。
B: I'm looking forward to seeing you again
盼望能再見到您。
look forward to中的to是介詞，所以后面如果接動詞的話要用ing形式。

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

Be sure to drop us a line=Remember to drop us a line.
別忘了來封信。
Remember to give us a ring
別忘了給我們打電話。
Don't forget to send me a message.
別忘了給我發短信。
drop sb.a line“寫信給某人”

Take care．
多保重。
A：Take care.
多保重。
B：Sure．Bye-bye．
我會的，再見。