It depends, if it says “best by” and then a date, that just means it’s freshest by that date and anything after is not going to really be as good, but is still edible. For example, if tortillas are past the best by date then they tend to be a little hard, but that won’t hurt you. If it says expired it usually isn’t very good to eat and may even make you sick. I know when I worked for a grocery store we would mark down anything that was past the best by date, as long as it was just within a year for some foods, and less than 6mos for others. If it has any kind of dairy we would usually toss it (like pudding, etc.). One thing we never would sell later was meat, that’s a hard no. Also, in terms of medicine, if they’re expired then toss them, they won’t hurt you, but they no longer work either so it’s not worth it haha.