You're really stocking up, but if you don't eat it all, it would be a waste.
この場合、次のような言い方ができますよ。
ーYou're really stocking up, but if you don't eat it all, it would be a waste.
「すごく買い込んでるけど、全部食べれないと勿体無いよ」
to stock up で「買い込む」
ここの「勿体無いよ」は It would be a waste. のように言えます。
ご参考まで!