I found eating out was actually cheaper than the UK.You're correct that for the country as a whole, food in the UK is cheaper than in the US.
However, grocery and restaurant prices vary enormously in the US from state to state and city to city. Grocery prices in the US are affected to a large degree by things like long-distance transport/distribution costs, relative local market saturation of large food retail chains, the health of the local economy, local social/cultural traditions, etc. Restaurant prices vary widely as well, so a traveller's food budget should take their itinerary into account. Fortunately, most restaurants post their menus online, so a tourist can do some comparison shopping, and should be able to save a few bucks without sacrificing quality.
Sadly wasn't allowed to browse many hardware sections - wife was not amused