It's difficult to prioritize supplements in general, as everyone has different nutritional needs. Everyone has a different lifestyle, stressors, diet, conditions, etc. which would indicate different protocols. That being said, there are some supplements on the market that are good for general well-being and health. A good multi-vitamin will act as your nutritional 'insurance policy', and one that contains multi--minerals would be even better. Zinc and magnesium are two minerals that many people are deficient in, so look for those on the label. Antioxidants are also important for fighting free-radicals (non-stable molecules) that could in turn damage your body cells. Your essential vitamins and minerals are anti-oxidants, but other great sources can be found in greens-type products, sea vegetables, grape-seed extracts and green-tea extracts. Combing a good multi-vitamin with one of these potent anti-oxidants would go far.
Essential fatty acids (like omega-3s) are also key, because they are essential to our health, but our bodies can't produce them. They must be consumed as part of the diet. A good fish-oil is a great way to ensure that you are getting a proper amount of omega-3s (there are some plant-based sources as well). Omega-3s support overall immune system health, your cardiovascular system, and even your nervous and musculoskeletal systems.
Extra Vitamin D is a final one you may want to consider, especially in the winter months. Research is being uncovered at a rapid pace that shows the importance of Vitamin D -- it's necessary for the absorption of calcium (and thus the prevention of osteoporosis), it helps fight infections, depression, inflammation, the list goes on...
Finally, your diet should be your number one priority. Focus on whole foods and avoid those with ingredients you can't pronounce or that your grandmother wouldn't recognize! Avoiding processed and convenience foods will also help keep grocery bills down.
Response by Greg Carver