"今のうちに食べちゃおう"
今のうち = while one can, when one has time, now that one has the chance
Let's eat while we can が "今のうちに食べちゃおう" に近いです。
Let's eat while we still have time — 時間があるときに食べちゃおう
例文:
Yay, it's lunch time.
やった、昼休みだ。
Lets eat while we can.
今のうちに食べちゃおう。