how to increase fats?

Till, now we may have heard how to maintain body fats, but, here, my discussion is on how to increase it?
What are the ways, diets to increase it..

Do you mean you really want to increase fat ? No body wants to increase fat, may be you want to increase your weight , are you too lean ?

Yes, I want to increase fats to gain a weight, since, my body is thin, and I can't even join Gym because of daily busy schedule.
So, want some solutions other than, which can be easy to manage in time or some fatty diet..