You should get some food in you before your entrance ceremony begins.
この場合、次のような言い方ができますよ。
ーYou should eat now while you have a little time.
「少し時間があるうちに、今食べちゃいな」
ーYou should get some food in you before your entrance ceremony begins.
「入学式が始まる前に、少し食べときな」
ご参考まで!
"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。