Chefs of Reddit: Ok for Canned/Never Canned?

What are, if any, things or ingredients that you would never buy canned or in a bottle or other pre-made condition, and what are things/ingredients that are perfectly fine to get canned or such?

I just hear often from people that "you should neeeever buy X canned" or "REAL chefs always makes x fresh" and blah blah blah.