How to gain weight fast?

cows feed their calves milk for fast growth.

so drink whole milk or even half and half with and between your meals.

you could probably gain 5 lbs.

Well... be careful with fast food because those chemicals will put you in a negative mood. And watch out for rice and bread unless you enjoy constipation. I have to eat like a pig or i just turn into a skeleton. Sausage, burgers, milk, tofu, chicken pot pie, ice cream. I love me some chicken pot pie. Gravy isn't too bad of a fat source. But keep in mind. Too much of anything can affect your health.

Eat..

Nothing. You can't change your basic health or your body type in 8 days. Not even close. It would take at least 8 months.

Also, a 13 year old shouldn't be trying to gain weight like this. It's not healthy. You will fill out as you get older.