How long can a sandwich, in a Styrofoam container, keep in a refrigerator before going bad (food poison risk)?

It would depend on the type of meat, the ingredients inside the sandwich, and how well it is stored inside a refrigerator. There are some things to consider, like the quality and freshness of the ingredients that were put inside the sandwich. Say for example, there is some old wilted piece of lettuce inside, that could act as a catalyst for encouraging bacterial growth. Generally I would say 3 days max from the package date is good, otherwise the sandwich isn't going to be as fresh anymore and might have some soggy bread.