Ok then, first off, here's a nice easy meal that takes a few minutes to make and will definitely help pack on the mass. Make 1 cup of oatmeal, add 2 tblespoons of peanute butter, next add 1-2 scoops of your favorite chocolate whey, and mix the shit out of it. There you go, you're done. It has a lot of protein, a lot of good quality carbs (lower glycemic too), and the fats in there are all essential fats.
Next off, eating frequently through out the day is the way to go, but try to have it balanced. Protein and carbs in each meal is a good idea, not to mention, the carbs will help to fill you up so you aren't so hungry.
Peanuts, pretzels, beef jerky, combos, etc. YOu know, all the stuff everyone else has said are all good snacks.
Good luck man and grow!