When I typed everything I ate into fitday.com for a few weeks, I found that even though I was eating a good Paleo diet, I was low on magnesium, manganese, zinc, and potassium. This isn't terribly surprising since grains are a good source of minerals.
I am not a fan of supplements, and only take them if I am pretty certain that I have a specific deficiency, and only until I think the deficiency is cured.
Also, I think the US RDA is influenced by the grain-based diets that we are "supposed" to eat, so just because I am low in these things according to the RDA doesn't necessarily make me believe that I need to have them.
So I wanted to supplement carefully, and took a magnesium, manganese and zinc supplement for a few days. I did notice an immediate improvement in sleep, mood and relaxation. I only took it for a few days and generally feel fine, I don't think I "relapsed". I make it a point to eat foods that are high in these minerals now.
I definitely wouldn't worry about supplementing vitamins A or B, and if you eat enough fresh fruits and vegetables, vitamins C or K. One serving of liver gives you your RDA of vitamin B for the week, for example.