There aren’t many summer jobs available for my young teenage son. Can he work in a supermarket where they have a nice kosher section, but it’s mostly non-kosher food? Are there certain jobs within such a place that are more or less desirable from a Torah perspective?
It is difficult to answer you properly without knowing you or your son’s religiosity background. In general, a boy in Yeshiva should learn or work in an Orthodox Jewish camp (a boys camp and not mixed with girls). A boy in Yeshiva should continue to learn Torah throughout the summer.
In any case, according to strict Halacha, one is allowed to work in such a market provided that he is not preparing cooked non-kosher food.
Regarding selling non-kosher food, since the Jew does not own the food and does not prepare the food there are many Poskim who hold that the prohibition of selling certain non-kosher food does not apply. There is no concern of possibly eating the non-kosher food when one is working in a market (and not a restaurant) where most of the foods are completely closed and can only be consumed when leaving the store.
However, this is not advisable unless one is pressed desperately for money. The biggest concerns would be possible fraternizing with women, Jewish or להבדיל non-Jewish, and possible Yichud situations.
Therefore it is highly advisable to try to find some sort of job in a Jewish camp as a first choice. It would be advisable to also consult with one’s local Rabbi or Mashpia.
A Jewish worker selling non-kosher foods that dose not belong to him – See Shu”t Shoel U’Mashiv 3:122; Shu”t Igros Moshe Y.D. 1:51.