"Don't buy too much food" 英文的完整句子可以这样表达：

"Don't buy too much food. It's a waste of money and resources, and it's not good for the environment."

这个句子的主要意思是：不要买太多食物，这是浪费金钱和资源，对环境也不好。

一些其他英文例句：

"Try not to overbuy food. It's better to shop more frequently and in smaller quantities." (尽量不要买太多食物。最好多去几次超市，但每次买的数量要少一些。)
"Be mindful of how much food you're buying. It's easy to get carried away, but we don't want to waste anything." (注意你买的食物的数量。很容易买得太多，但我们不希望有任何东西被浪费。)
"It's important to only buy what you need. Don't let yourself get tempted by sales or discounts on food that you don't really need." (只买你所需的东西很重要。不要让自己被食物的销售或折扣所诱惑，如果你真的不需要。)

这种建议的来源可能是出于环保考虑，因为购买过多食物可能会导致浪费和过度消耗资源，从而对环境造成影响。此外，购买过多食物也可能会导致财务上的浪费。