I would agree that whole milk is about the cheapest relatively healthy source of calories. If you can get down 2 litres each day (spread out) on top of your normal eating, you are bound to gain. Nuts are good too. Peanuts are cheap but best go for the unsalted type (or wash off the salt) if consuming a lot of them. 150g of peanuts plus 2 litres milk works out at about 2,200 cals.
7 years
