How do i gain weight at low cost in this situation?

Im a very light weight guy who does labour work and all i have is muscle and bone, no fat at all. When i look at my body it looks like skinny Bruce Lee. Im 20, my height is 179 cm and i think my weight is around 55kg or something which is considered underweight for my height right?

Ive been eating once or twice a day but i dont think i will ever gain weight at this point due to my smoking habit and drinking sometimes. I thought i could at least get beer belly but i just burn away all the calories in a single day at my work no matter how much beer i drink.

Last few days ive been eating cereals but i feel much weaker now. So I’ll just go back eating chicken breast. But im getting really sick of those bland chickens though.

How do i gain weight at low cost in this situation?