4 pounds would be 3500 * 4 = 14,000 above what you need to stay even for 2 days, so about 17,000 calories in 2 days. Something like 4 pounds of hamburger, 2 pounds of cheese and 2 pounds of butter would come close to doing it. Spread out over time, it takes less than most people think to gain weight. In a short amount of time, it takes more to gain weight than most people think. When this is really important is if you have a binge/setback - a lot of people throw in the towel and start gaining big time again when the setback would have been a half pound or so. But the immediate effects due to water and increased food in the gut is much higher and people freak.