How can I gain weight?

I'm an underweight skinny mofo..

Sitting at home all day is not an option.. I enjoy the outdoors.

Eating ridiculous amounts of food isn't an option either

What are the remaining options? I envy fat people losing weight cause they can just get surgery and remove it..  is it possible to get fat transplanted from a fat person?

Kettlebells.

They will give you a 20% increase in muscle mass and weight if you are under weight.

Also a 20% decrease if you are over weight.