祝你玩得开心/ 玩得开心一点

Actually , in the daily life of Chinese people , we're not used to say something like "have a great day " or " good luck " to our friends when we say goodbye to each other . But it's okay if you want to press good wishes to your friends, you may say 过得愉快 or 祝你一切顺利。Or just say 保重！

今天顺利！这才是标准的说法

You're very welcome Galaxy. Chinese is an amazingly rich language, a real joy to learn. Feel free to contact me about any such phrases and their translation into English. Good luck with your studies!

祝你玩的愉快！ 好好玩咯！