You can say: "Chúc chuyến đi vui vẻ!", hoặc "Đi nhớ qua mà về nhé!"

You still could use some sentences Translated from English, example: Enjoy! Have fun!

Here it's quite different between those who you're close or not because you can talk funny things with your close friends instead. But for all situations, you can use "Thượng lộ bình an" (this is a Sino-Vietnamese sentence that means you hope that one will be safe and have fun for his or her trip) or else "Đi chơi vui nhé" And for "Tối chị đi xem phim", you can say "Xem phim vui vẻ nhé" In fact, if we translate word-by-word from English into Vietnamese for these cases ("have fun" or "have a nice time/day"), it'll sound fake or loath. So, it's quite flexible to use Vietnamese in cases :)