- A good set of multiple vitamins and minerals to avoid any nutritional deficiencies.
- A good protein powder to take in between real meals so that it is easier and more convenient for you to increase your protein to the levels that you need. A good 5lb tub of protein from a reputable company like Prolab, Labrada, or 8-Ball Nutrition will do the trick. If you need to gain weight however because you are a hardgainer, then I would go for a high quality weight gainer. I like Prolab's N-Large 2 and Labrada's Lean Body Mass 60.
- A couple of tablespoons of good fats such as flax oil or natural peanut butter. You can add these to your shakes.
Definately, stay away from any testosterone boosting supplementation. Right now (since you are a teenager) your body produces a ton of anabolic steroids (testosterone and growth hormone mainly) that will greatly help you in your quest to build muscle rapidly while losing body fat. Anything that you do trying to further boost your testosterone production may do the exact opposite. Save testosterone boosters for when your body starts to slowly decline in testosterone production, which is around 25 years old.
The supplementation program above, in conjunction with a good bodybuilding diet (see this sample bodybuilding diet), a good training program (see my bodybuilding routines page), rest and the determination to execute your bodybuilding program day in and day out will take you to where you want to be.
If budget allows instead of a 5-lb protein tub, you can opt for easier to carry and more convenient items like Meal Replacement Powders or Ready To Drink Shakes. However, convenience comes with an added cost so if budget is tight, simply carry the servings you will need of your protein powder individually sealed on a ziploc bag in your cooler and mix them with water or milk when it is time to consume. You will need a shaker bottle for this but all high quality proteins these days are instantized and therefore mix rather easily.
Take full advantage of your age. One of the key elements to my bodybuilding success, I feel, is the fact that I started bodybuilding training at 14 years old, so I took full advantage of my natural steroid production by training and dieting hard day in and day out at the age where you get the most gains from your efforts.
Remember that the real key to long term bodybuilding success is the consistent execution of your training program, your diet, your basic supplement intake, and last but not least, getting your rest.
Best of luck!