This is a pretty narrow question compared to the other tribal ones that will follow, but it does tap into one core aspect of the pegasi - how their magic detaches them form the other tribes. So as well as answering directly, feel free to talk about cloud cities and the "sky world" in general. Oh, and we might as well put pegasus magic discussion in here too, just for neatness.

I'll just answer the title for now.

Food production in Cloudsdale is ... not technically impossible, but certainly not practical on a sufficient scale to feed the city. But the same can be said of any city really; what complicates Cloudsdale's supply chain is that it moves, and can therefore not draw from any one set of farms and villages. Supplies of preserved food are laid on in bulk and supplemented by surplus from nearby towns, giving the city it's ... unmistakable culinary character.

Either despite or because of the large food stocks, weight is at premium in Cloudsdale; any non-cloudcrafted item is taxed on it, which fuels both the cloudcrafting industry and a somewhat unmaterialistic lifestyle for most inhabitants, who focus on accumulating experiences rather than things. With Cloudsdale being a center of pegasus culture, this sentiment often flows outwards to places where it has less practical relevance.

Definitely. I fear elaborating on this any further is just going to end up in me spouting Fallout: Equestria canon. :B But guaranteed it's really hard to grow ground crops in the clouds, not least of which is because you can't easily get earth ponies up there to tend to them. I'm sure the pegasi attempted to gain agricultural autonomy way back in the way back, but the great difficulty associated with cloud cropping means they probably still import most if not all of their food from the ground.

10. Are there foods or items native to Cloudsdale that are uncommon on the ground? Are there foods or items on the ground that are uncommon in Cloudsdale?
Weather-related items like rainbow juice are uncommon on the ground.

If Cloudsdale can produce any kind of food it must be uncommon or else the pegasi wouldn't have been starving in the Hearth's Warming Eve tale.

Cloudsdale is a cloud; it can't grow anything. However each type of pony would have different tastes. Pegasi would eat things that are very light, like birds do, because bloated stomachs would make them feel uncomfortable when flying. Earthponies would eat heavy things high in calories because they are far more interested in moving around all day, and their fortitude would keep them from feeling bothered by a heavy stomach. Unicorns as a whole are far too concerned with their own endeavors to concentrate on preparing food, unless that is their talent. Bookworm unicorns would have invented the smoothie because they are too busy to eat, and socialite unicorns would have refined the various recipes of the Earthponies and Pegasi.

As a preamble: I like pegasi.

That being said... I think they might have a far-reaching history of being thieves and muggers. They would probably kick some teeth in for such a statement and they would most certainly refrain from calling it that, but... Cloudsdale is a cloud. It's a nice cloud, sure. But it's less than ideal for any kind of cattle or plant matter. It's windy and freezing cold and there's no soil to gain nutrients from. And cities without food supply don't tend to remain cities for long.

In the Celestial Age, under Celestia's sole rule, and as far back as the founding of Equestria, things were easy enough. Everypony cooperates, trade flourishes, and food is a simple purchase away. Yaaay.

But before that? They were a militarily structured people. They were warriors. Can't fight on an empty stomach, food's gotta come from somewhere. Some unicorns might have talent in growing stuff. Or shooting it with magic until it grows to house-size and starts talking. But would you really want to put that into your mouth? That tomato surely shouldn't glow. Especially in that color!

Earth ponies grow stuff. Tasty stuff, in decent quantity. And I find it difficult to find other explanations. Sure, they might have bothered others as well to sustain their city. But when you have the choice to mess with a bunch of very angry griffons who will follow you back home or some earth ponies that can only yell at you once you retreat with their food, who are you going to pick?

I think the pegasi might have been a menace on earth pony villages back in the day. Heck, I can even see earth pony villages hiring unicorns to defend their warehouses with fancy magic. Until the unicorns get greedy and double-cross them, or raise their prices, or demand food themselves, or-... well, you know. Scholar's have to eat, too. And those glowing tomatoes really don't look all that enticing.

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As a preamble: I like pegasi.

Me too!

And yeah, we know that they relied on earthpony-grown food from the Hearth's Warming story. How willingly it was given... well, that's perhaps lost to history.

(I don't think they had real cloud cities back then, to be honest, but high-mountain ones still aren't the best for faming.)