TSA has no restrictions on bringing vitamins in pill form and powder supplements in your checked luggage or carry-on bags. You can pack these items in their original packaging or transfer to pill organizers. You won't need to declare or show them to TSA agents when going through security.
You can safely store most medications in the same organizer compartment with other drugs for short periods of time without them interacting. But check with your doctor or pharmacist to make sure. Also, make sure your pillbox is filled correctly.