Hallo Tim,
Pork product such as bacon,sausages and ham are only sold in a few shops and are expensive. Cheddar cheese slices are available in packets but not a block. I bring powdered jelly as the jelly is not so nice here. Marmite, Branston Pickle,custard powder,Oxo cubes and baked beans are available but cost more than Britain.
Bread, fruit,salad and vegetable are easy to obtain and there are loads of shops which sell the basics.Steak, lamb, chicken and offal are also easy to find and reasonably priced.
Have a good holiday.