A lot of the food you might take averages out at about 100cal/oz, so 2 lbs a day gives 32 * 100 = 3200 calories. This is about what a "typical" 15-30 year old "active" male adult needs.
Typical 15-30 year old males can't be bothered to analyze food and add it all up. Hence the 2lb/day rule of thumb.
If you have no personal experience to plan by you can use that table to adjust the weight of food you should plan to take.
Obviously you can be more weight efficient if you want to take the time to design your diet emphasizing food that has higher cal/oz. Nuts and oils like tend to be about 200cal/oz. Things you want to take for taste or some specific nutritional quality might have much less than 100cal/oz.