Supplementing your diet with protien and a good multivitamin are undeniably and absolutely necessary. There is no way that the human body, especially trained at the levels of fitness enthusiasts and strength athletes can meet it's nutritional needs by simply eating food. I mean, do we really have a conceptualization of how much food we would have to eat to get a complete/full spectrum of all the vitamins and minerals necessary for healthy human development and maintenance? It would be impossible to consume that much food - we cannot handle the volume and if we could, we wouldn't have time in the day left to do anything else but eat and digest. Not to mention nutrient timing and optimization due to bioavailability...
Aside from protien (I look to meet about 300g daily) and a solid multi (I take two one-a-days), I would advise additional supplementation with BCAA's (additional branch chains such as Leucine and Ornithine can help stimulate growth hormone signal), Arginine for NO2, Glutamine for recovery and a glucosamine/chondroitin supplement for your joints.