You can walk down the isle of just about any pharmacy or chair grocery store and just pick them off the
shelf, but is this the smart thing to do? Did you know that supplements are not in any way regulated by the Food and Drug Administration? Therefore, the quality can vary considerably between one brand and another. One very general rule of thumb is to buy the store brand of large, national chains such as CVS or Publix's. Why? Because, supplements are a large profit center to these chair stores and if it should appear on the news that their Vitamin C 1000mg is not Vitamin C 1000mg they stand to loose a lot of money.
A second reason to be careful before you just pick a supplement off the shelf is that supplements can negatively interact with other supplements and, most importantly, with prescription drugs. Here, on Pine Island, if you purchase all your prescription drugs from CVS pharmacy, they are more than happy to tell you if a supplement will negatively react with other supplements or prescription drugs you are taking. Just ask! (They also staple information about your prescription to the bag. Do you read it?)
Another resource is the internet, read up on a supplement before you purchase.