In addition to food, the UK also imported farm machinery and weapons from the US. The UK couldn't afford to pay for it, so the Americans introduced a system called "land lease". The UK made the final payment in 2006.
Until 1942, the UK also imported from Australia, New Zealand and the Far East, although supplies were disrupted by the war in the Pacific. The Soviet Union also imported from the allies.
Despite the mythology, the UK never did stand alone in the war. It was extremely dangerous for the merchant seamen involved, but most convoys did actually get through. If they hadn't, the UK could not have continued with the war.