I think they will make you open a random sample of whatever you take. I took food which I had cooked myself in a tupperware, they made me open it and taste it. Could you put them in a tupperware once they have been opened, in a cool bag they'll be ok for a while?
Yes you're probably right, they will make me open them won't they? We are flying out of Heathrow. I will just leave what I bought at home and try to buy something at Boots on the other side. And of course also pack sarnies.
Really looking forward to a transatlantic flight with a 1 year old and a 2.5 year old :-) At least there will be one adult for each child!