Gainers, shakes, mixes all really should be used if you can't fit in whole food. Buy a shaker/mixer and buy grains that can be diced up. Make a shake that includes whey or casein (depending on span of time) with rolled oats, whole grain granola, mixed fruit (ones with higher fructose to glucose ratio), some nut butters like that of almond or peanuts and even some nuts depending on mixer options.
It's easier than it sounds. Set it up in the beginning of the day for when you know you'll be short of time then add water and press the button. You should have the ingredients in your diet anyway so this would be a bit more cost effective.
But if you're going to reach out to supplements instead of nutritional needs...look into ON Serious Mass. Jam packed with carbs, just probably 1/8 of it includes simple, quick insulin responsive sugars. So that's a con...more peaks and valleys with insulin the more resistant and more likeliness of fat gain to occur.
Hope this helped