Slight tangent: we caught a bit of a morning news show when we were in New Zealand where this exact question was put to Kiwis living abroad. The hands-down winner? Chocolate fish. 
As a result, I bought some. They were shockingly unremarkable. I’m assuming that the poll was skewed by Cadbury shills.
As for the OP, I’d have to go with Mexican food. I love me some good Mexican.
Rutabagas. My local, hardly top-shelf supermarket carries them.
When I was in India, I really wanted a beef burger. Maybe it had something to do with all the cows walking around.
And I found myself in desperate want of chocolate chip cookies or really any other cake-like dessert that wasn’t based on milk solids.
Huh? I used to eat it regularly. That said, it is very seasonal.
In n Out.
Mexican Food in general.
I never saw it at Oxford. Maybe I wasn’t going to the right places or something. I know I never saw it in the Cornmarket.
I’ll have to ask at Wegmans (if anyone had them, they would). Haven’t seen them around the turnips and other root vegetables lately.
Getting the kids to eat them is going to be more of an uphill battle, I think.
When I went from Philadelphia to New Mexico, I missed readily-available soft pretzels, Turkey Hill ice cream, and more than anything I still miss Tastykakes (like Hostess products, only a million times better).
When I went from the US to Ireland and then the UK: Peanut butter. I’d always taken for granted that I could go out and buy terribly sweetened peanut butter, or low-fat peanut butter, or organic no-sugar-added peanut butter. You can’t do that in Europe. Also: iced tea.
And when I’m anywhere but New Mexico, I miss green chile. I don’t even like it that much, but it’s omnipresent here, and apparently doesn’t exist outside of NM.
In the event we have to evacuate the country after Sarah Palin is elected president in a couple of years, you will NOT be allowed on the bridge or near any of the ship’s computers.
I would miss Milo and Vegemite if I were to ever move away from Australia. Apparently Twisties are hard to find overseas too. Not my Twisties!
Sainsbury’s and Tesco’s sell it in the vegetable aisles.
Really?! There’s no way I could have missed that for seven years…maybe I’m just having a mental block here. I seriously don’t remember it at all, and anyone who knows me knows my voraciousness regarding corn on the cob, which would probably would be my last meal if I had to have one. Hmmm.
I picked up this habit from my husband who was born & raised here (I’m from away).
Beans and brown bread are a staple New England working class dinner. When you’re flush with cash you add a slice of fried ham alongside.
The husband has a lifelong horror of raisins, though, so I’ve never had anything but the plain, and always B&M brand.
I’m not even in another country and I have a constant craving for chistorra… it’s a kind of red sausage; in theory it’s available here, but they don’t know how to cook it. It’s as if they cook it by ear, like someone has told them how to do it but, never having seen the real thing, they don’t get it right.
Other times I’ve missed the oranges (Navels and Navelinas are the juiciest but, being “ugly”, they don’t get exported as much as the prettier varieties), specific cuts of meat (the pork one called steak in the UK, but left as a whole almost-cylinder for roasting) or, of course, serrano.
Depends on where I am and what’s available, I guess. I didn’t miss avocados when I lived in Israel, because they were easily obtainable, but I would have killed for one when I lived in Bulgaria. When I lived in India, I craved apples, which were kind of hard to find. (I did eventually find them, but they were more expensive than the tropical fruits I would usually consider a special treat, like mangoes.)
But basically, and I guess this mostly goes for Bulgaria:
Mexican food.
Cheese. There are two kinds of cheese in Bulgaria, sirene (which is like feta) and kashkaval, a mild yellow cheese. Both are okay, but it got boring fast. In Bulgaria, I lived about an hour and a half from Plovdiv, the second biggest city in the country. In Plovdiv, there is a fancy imported meats and cheese store. I GOT CHEDDAR THERE. It was so fucking exciting!
Tofu.
Broccoli. Why was is impossible to get broccoli in Bulgaria? * Why?*
Asparagus. Ditto.
Spinach. Available during a two-week harvest season once a year. Bah.
Bagels. BAGELS.
Breakfast food! Cereal I could get, but I wanted to go out for fucking breakfast and get pancakes and scrambled eggs. NO.
Premade food. I am lazy. I want to microwave something from Trader Joe’s. No. Everything must be made from scratch.
Fake meat things. I just wanted a veggie burger!
Basically, I ate a lot of food when I got back to the US.
I have a list this long of food I miss from Bulgaria, too.
I’ve been thinking about this, and I think these two things would definitely be my top two as well. No fresh mozzarella? No bacon 1st thing in the morning? Shoot me now…
From the UK to the USA, there’s only one: marmite.
US to Canada
From the South I miss Eastern North Carolina Barbeque, hush puppies, and oh, my, god, Boiled Peanuts. In the interest of muliticulturalism I have taught the Attackkids to pour salted peanuts in to coke and drink it from the bottle.
Mexican food is almost impossible to get in the area where I am now, although I stumbled into a real good place in the interior of BC a while back.
Remotely decent Mexican food does not exist east of the Atlantic. I missed it when I was over there.
I learned that from here. It’s not bad.