^All of this.
Eat lots of meat and vegetables, some fruit, dairy if you like. Peanut butter is a good idea; one simple way to add weight is "Eat everything you normally eat, and before bed have 1 cup of whole milk with a mighty glop of natural peanut butter and a frozen banana." I would stay away from sugary stuff in general, but since you need to gain weight and you're probably training pretty hard, you might be able to get away with some crap (cereals, pop tarts, ice cream, stuff like that) if you're having trouble putting weight on.
Supplements are not critical, but at your age I would recommend a simple whey protein powder first, with creatine monohydrate next.