"Food" can be countable ("a food", "many foods") or uncountable ("some food", "a lot of food"). The countable sense is used to refer to a particular type of food, or, in the plural, several different types. The uncountable sense means food considered as a general "substance", without particular regard to the varieties it can come in. 

My job is to protect fish, vegetables and food from going bad.

This sentence is poorly written in my opinion. It reads as if fish and vegetables are not food. It should be:

My job is to protect fish, vegetables and other foods from going bad.

"other foods" means "other types of food", which is the sense wanted here.

I am a box in which foods, medications, and chemicals are kept cool. 

In this sentence, either "food" or "foods" will do. To me, "food" is better, since there is no need here to emphasise that food comes in different varieties.

I use many creams/oils/detergents.

This is fine. The same concept applies: "a cream" is one type of cream; "creams" means several types of cream. Similarly for the others.