I had the same experience in Budapest. You almost never see a black person on the streets of Budapest (not to say you should expect to), but coming from an American city that is almost half of African decent, it was an odd thing to get used to. While there are pockets of Chinese, Roma, and Turks in the city, the city is fairly homogenous by my standards.
I picked up my brother from the airport after he had spent several months in Japan back in college. He asked me to drive directly to the nearest donut shop, where he purchased a dozen donuts, all for himself. 
I lived in South American for a little while and the things I missed most were:
- Unlimited hot water in showers (plus uniform temperature throughout)
- TP you didn’t have to pay for (though this was minor if you had the presence of mind to carry a little travel packet of tissues)
- Central heating - I don’t mind sweating too much, but in Chile it can get surprisingly cold in the winter. My space heater ran out of gas early in the winter and my host mom “forgot” every week to replace it, so I used to put on two pairs of pajamas and toss all my available clothing and towels on top of my blankets before bed and I’d still be cold. I could see my breath in my bedroom.
Comfort food was easy enough to come by. I think the only place I’ve missed American-style food was when I recently spent a month in India with my husband’s family. I rarely eat meat, and when I do it’s usually chicken or fish, making beef a rareity. Still, I was eyeballing the sacred cows with evil intent by the time I left. Had we stayed too much longer, I might have embarrassed my husband by trying to chomp on a live cow. Next time I’ll eat beef for a week or two before we leave the country.
I was warned about the squat toilets in India, but actually found them a LOT cleaner than most seated public toilets anywhere. At least your rear doesn’t have to touch anything. I also didn’t miss regular showers vs. the bucket and pour mug method - not only did I wind up wasting less water, I also was able to get the water to the perfect temperature before dumping it on myself. If they constructed bathrooms in the US the same way they do in India, I’d probably choose a bucket and mug shower over a showerhead most days.
Crud, missed the edit window. I thought of another thing I missed in India: US baked goods like brownies and cookies. My husband’s family ate primarily milk-based desserts, like rice pudding and candies made of milk solids, such as burfi. I know they have biscuits and chocolates in India, but it would have been rude to ask for something else - I was a guest and they’d never met me before. I have huge texture issues with milk-based foods. They don’t make me gag, but make me want to immediately spit out whatever it is I’m being fed. I made a huge batch of cookies after the jet lag wore off and ate way too many of them.
I did acknowledge that mine was a tourist’s view. And I haven’t left the country much this millennium.
Back when I was your age, of course.
We kept to the touristry country-side in Ireland; there was no way I was going to drive in a city in Ireland. The cows are quite tricky enough, I was not going to attempt dealing with other drivers.
Interestingly Ireland’s immigrant population although centred mainly upon Dublin is quite spread out across the country. For example, half the population of the town of Gort, Co. Galway are originally from Brazil. My impression of much of the US is similar to your impression of Ireland. Outside of Chicago and NYC, the places I’ve visited have felt less polyethnic and multicultural than my home town. There are Thai, Japanese, Chinese, Indian, Polish and African restaurants or stores within a 10 minute walk of my house.
Air conditioning. I love coming into the cool on a hot day.
Barbecue, sports scores, cheap fatty/greasy take-out food, my house (I bet it would be impossible to find as much room and land for anywhere near a reasonable price wherever I moved, assuming it wasn’t the Congo, and that would present another set of problems).
NPR. Seriously - there are three great radio services on Earth: NPR, CBC, BBC. (I’ll give a courtesy shout-out to RFE/RL).
Internet streaming or no, I’d be unhappy living outside the reach of one of the Awesome Three. Ideally NPR.
The thing I missed most traveling is drinking fountains. Public drinking fountains, with marvelously chilled, potable water. Getting through customs in the Frankfurt airport, and feeling thirsty. Then, where is water? Where are the fountains? None near the bathrooms. What? I have to buy water? There’s no free, public water? NOOOOOOOOOooooo
In Amsterdam I got nailed for not weighing my produce before I queued up at the cashier. I was ridiculed. “I suppose in America you get someone to bag your groceries too, huh?” Well … yeah. That stuff was no big deal, just kind of shocking that I failed to notice what was expected and was treated pretty shabbily for it.
I’ve never understood how Americans are so keen on drinking fountains, but so squeamish about other aspects of public sanitation in foreign countries. There used to be a few drinking fountains here and there in this country, but they have died out. Who wants to drink from a scummy public tap that anybody might have touched? I have fresh water on tap at home, thanks.
*being able to put dirty clothes in a machine and forget about them until they are clean
*English books/bookstores
*fast mail delivery
*being able to take something out of the freezer and have dinner in 5 minutes or less
I’ve been putting a lot of thought into this lately. 3.5 months until Madagascar!
Oh, let’s see. Things I missed. Decent Mexican food, a good hamburger (Ground beef. Cooked (Belgium was a tad twisted in this respect)). Window screens. Universities where the books are mostly in one building which is open, like, 9-5 M-F, rather than 2:15-4:00 on Tuesday. High speed internet. Convenient laundry facilities.
There were a lot of things there that I miss very much now, too, however.
While I know An Gadaí mentioned plenty of non-white ethnicities, in my trips to Europe(every 2-3 years since the early 80s) I’ve noticed one difference in perception that might cause some confusion. Europeans frequently think of multiculturalism in looser terms than Americans do(in my experience). A European might see a multicultural group of Germans, Poles, Spaniards, Frenchmen and Italians, while an American will look at the same group and just see a bunch of white people.
I have lived in other countries. Our basic freedoms are what I missed the most. As much as I loved living overseas and learning about other cultures and making friends, I was sooooo happy to come home!
In my experience Western Europeans are treated slightly differently than even Eastern Europeans. They are less ‘other’ than the newer EU citizens and those from beyond the EU.
When you’re traveling, home can be very far away.
The majority of public fountains in America are hardly “scummy.” Probably your own sink is scummier.
For myself, I’d miss Wegmans.
I’d miss bagels. Depending where I go, I’d expect to miss sushi. There will be a lot of things I’d be considering trying to get care packages of - since spice mixes don’t often travel across national boundaries.
I’d probably miss New England style weather - though Ireland is pretty close from what I’ve heard.
I’d miss reliable postal service. (In most countries, at least, I stand by the assertion that the US Postal Snail is better and more honest than about 85% of the countries out there.) I would miss reliable phone and intenet and power service.
I would miss smoke-free areas.
I’d miss my anonymity - being noted as “That Yank” would bother me a lot.
Lenders are not bagels. I’m not sure what they are. They’ve even tried to mimic the whole “donut dipped in cement” with a stunning degree of success, but they’ve missed the whole “flavor” thing.
It is possible to find excellent bagels outside of NYC. But it takes dedication and determination. And slogging through a whole mess of alleged bagel-like things to find them. More often than not I find it’s not worth the effort - and just stop a the first “good” bagel I find.
The next time I’m in NYC, however, I will be stopping at H&H on 80th. sigh
Bagels are increasingly popular here for some reason. I don’t get the appeal. Round bread with a hole in it. I’d prefer a sandwich or a roll. 
If you aren’t including “crusty, chewy” in your integral mental description, An Gadai, you’re not getting the real thing, yet. 