Gaining

1000 calories an hour

Lots and lots of cheap $1 burritos
2 years

1000 calories an hour

Doing it for a few hours wouldn't be too hard, but your stomach can only process food down to your intestines for so long, and then your intestines gradually fill up too. Besides which I've seen it estimated that we'll only absorb calories up to about twice what we need in a day, so there is only so much fattening benefit.

That said, if you just want to see how long you can do it for, for fun, it should be pretty straightforward, other than having to not go too overboard for the first couple of hours when it is easy.

Sweet baked goods are loaded with calories. A smallish cheesecake (the kind you buy frozen at the grocery store) is typically around 1500 calories. Pop tarts are about 200 calories each. Muffins can sometimes hit 500.

But you are apt to get bored of always the same thing. I'd do something like plan out a big breakfast that has a thousand calories, for hour 1, then have something sweet (cookies, pop tarts, whatever) in hour two, try cheese cake in hour three, fast food lunch in hour four, etc. Half the fun would be mapping out all the foods!

Cream has pretty intense calories. Half a cup of heavy cream would be between 350-400 calories if I remember correctly (although it is awfully filling), but that is one way to toss back some intense calories later on when you are getting full and it is harder to keep eating.

Clear, sweet, drinks don't really fill you up (your body absorbs the sugar but thinks it is drinking water, roughly speaking). Not the highest calorie source but kind of 'free' in terms of your capacity. A cup of apple juice has a bit over a hundred calories (depending on brand, I'm sure), so you could eat 900 each hour and use a cup of apple juice to help wash it down.

You do want your digestion to move along as well as possible, so I'd suggest taking regular walks to keep your body moving. Might get harder to go do as you get really stuffed, but at least for the first while.

If you give it a try I'd be interested in hearing what you do, and how long you could keep it going.
2 years