3000 seems easy enough. i think i racked up 1,250 yesterday with two lean cuisine frozen dinners, two handfuls of triscuits and a couple beers. (300 for each meal, 120 each handful of reduced fat crackers, 150 each beer) the actual, physical amount of food (supposedly healthy/reduced fat) totaling that 850 food calories was smaller than a usual dinner if either the Mrs or I feel like cooking. it was not much at all.
if not paying special attention to cut calories (no mayo, eating turkeyburgers/bacon instead of "regular", eating brown rice instead of whtie, wheat instead of white bread or pasta), it's easy for calories to rack up. hell, just your salad dressing or some sammich toppers are as bad as a 12oz can of beer. Two tablespoons of Ranch Dressing - what you might put on your salad is 148 calories. a can of Dale's Pale Ale, my current favorite casual beer, clocks in at 150. A 12 inch meatball sub (no cheese) from sammichway is over 1,100.
as for athletes, guys like Michael Phelps consume 12,000 calories a day while training. he's on the extreme high end, though.