I wouldnt worry to much, I've taken food for our use over for the last 4 years, touch wood had no probs. And have done when gone to Spain in years gone by and used my old tatty cool box.
just check how many cool boxes are on the luggage belts when you're in a queue to see how a lot of people take food over.
i dont go mad take usually take, 2lbs bacon, couple packs sausages. carton longlife milk, couple bottles of juice and cereal and Teabags. to tide us over the first week, then we dont bother so much the second week.
You cant buy decent dilutable juice abroad, you get that princes juice with red bits at the bottom, or pay a small fortune for something recognisable, or buy that Tang powdered stuff.
then on the way back i put some pressies in it, like boxer shorts or belts if we've bought them and usually haven't gone over our allowance.
The breakfasts although cheap n cheerful aren't always that nice, the sausages have always been horrid hotdog type sausages.
Alas cant go to Turkey this year