I suggest that you go online and look for American food companies in the UK. They import food (not make it there) and so you will have your favs. I have friends who order from
www.cybercandy.com [nofollow] and
www.skyco.com [nofollow] and
www.americansoda.com [nofollow] all of which import American foods, sodas, candy, baking ingredients, etc. It is expensive but to be honest, it beats the hell out of doing without. You could also have someone send over things from the States.
You can get Shake and Bake online. Actually I think Harrods and Harvy Nicks both have an American foods section (which are imports) and CyberCandy has a shop in London.
It may help to get the spices and staples and then use local produce. One thing about the beef in the UK, buy organic. The beef there has a lower percentage rating of meat than is required in the US. 100% beef in the UK means that 100% came from the cow...NOT that 100% came from the meat. It changes the taste dramatically. Butter there also has a higher fat content so remember when you bake that you have to reduce the amount of butter that you use by about 1/4 or it will be a greasy mess.
I guess all in all, if you can order staples and comfort food from the States or an importer you can make due with local produce.
Best wishes hun, it can be a fun place to live but it is a tough place to eat.