比較中規中矩的

Wish you a bright future and a happy life!

祝你前程似錦，一生快樂

如果情真意切一點，可以

I will cherish all tne memories of us together!

我會將我們的美好回憶永遠珍藏

再就是諺語和套話了

A friend is a gift, whose worth cannot be measured except by heart.

朋友是一種只能用心去衡量價值的禮物。

Congratulations on your graduation! Whishing you a future filled with success and joy of seeing your dreams come true.

祝賀您的畢業!希望您有一個成功的未來，感受到夢想成真的快樂。

Think of me sometimes while Alps and ocean divide us, but they ever will, unless you wish it. (Byron)

長相思，天涯海角；情不斷，山水難隔。 --拜倫