Ideally, you could get everything you need to stay healthy from good food choices. Practically, it takes either enough time and skill to grow, gather or hunt for it, or enough money to pay someone else for it. You may not have enough of any of these resources, and smart supplement choices can help fill in the gaps left by even the most sensible of modern diets.

Problem is, there are tons of choices in supplements out there. Which ones are smart, and which ones are just snake oil? I'm no expert, but I feel pretty comfortable with essential nutrients, so here's my take on a few:
Cod liver oil
Vitamin A
Vitamin D