Weight gain and loss has little to do with exercise and much more to do with calorie consumption. Excercise is more about muscle development and nerve restructurimg, with a combination of diet and excercise leading to the fat/muscle ratios coveted by athletes, body builders and health nerds.

If you are looking to put on weight but don't care about what kind of weight it is, the fastest way is low excercise with a high carb diet. Pasta is generally the cheapest thing I can can think of, but lots of rice can do the trick too. ("Bread makes you fat?") Sugar is a good way too, but your body tends to burn through it in an average day instead of converting it to fat, unless you are consuming bags of candy on a daily basis, which is expensive, unhealthy and can potentially lead to diabetes. Stick to high carbs, imo.

However, if you are looking to put on muscle, it's a little more tricky as muscle doesn't grow all that fast. But what you should do is focus on high fat proteins such peanut butter, and also just add protein powder to basically everything.