店の食べ物すべて食べつくすかもと思ったぐらい沢山食べてたって英語でなんて言うの？

ご質問ありがとうございます。

この場合、友達について、「店の食べ物すべて食べつくすかもと思ったぐらい沢山食べてた」を言いたいなら英語「My friend ate so much I thought he/she was capable of eating all of the restaurant's food.」と言えます。

ご参考になれば幸いです。

"店の食べ物すべて食べつくすかもと思ったぐらい沢山食べてた"
- They ate so much I thought they would eat all of the restaurant's food.
- They ate so much that I thought they might eat all the food in the restaurant.

They -> he/she

I went to an all you can eat with (friend's name) and they ate so much I thought they would eat all of the food in the restaurant.
- (友達の名前)と食べ放題に行ったら、店の食べ物すべて食べつくすかもと思ったぐらい沢山食べてた