Im not so sure it's impossible! 
I recently visited a friend down in Surrey who has just moved over here on a corporate relocation. I foolishly took her a small bag of goodies from Lupe Pintos, thinking she would be missing certain things. 
I was BLOWN AWAY when i saw the inside of her cupboards, and fridge... Bisquick, Betty Crocker cake mixes, Rice A Roni, Kraft mac & cheese, a hundred packets of taco seasoning mix, tins of Rosarita refried beans, Mrs Butterworth, Karo, Peter Pan peanut butter, Hidden Valley ranch dressing, Jiffy cornbread mix, Marie Callendar cornbread mix, Sue-Bee honey... cant remember what else, but there was NOTHING British in her cupboards except milk, cheese and bread.

I too have been blown away with some people that were in the Oil game and were on expenses. One family I knew (both expats) was unreal (maybe the same family 1/4Gill). They did all their grocery shopping at the local American Food Store. They bought things like Corn Flakes, ketchup, flour (not Bisquik which you can get here now

), even sugar (the plain old white granulated stuff

). We're not talking military commisary prices here or even UK High Street prices, we are talking speciality shop prices. Everything in their house had been shipped across, ice box, tv&video and all the tapes (no cds in those days), beds, I mean every thing. The kids even went to the American school (grammar school age not high school age). I always thought they missed out on a very unique opportunity.

There are a few things I can understand buying on special occasions like root beer (used to get it in Asda but they stopped), candy (though I can get Reece's Cups in Woolies now!).
I could tell ya some tales of military people that have been here for a 2 year stint and never left the comforts of 'little America'. Now that was BIZARRE.