My favorite bulking foods are eggs, eye of round roast and potatoes. Eggs are great because you can hard boil them and easily scoff 4 or 5, yolk optional, on your coffee break or whatever. Eye of round is the cheapest edible(IMO) roast available and is fairly low fat for beef. It yeilds like 50 grams of protein per 8 oz serving so the average 5-6 pound roast is good for 500-600 of protein. Potatoes are potatoes, great microwaved of baked, add a little cheese for flavour now and then.