Two things definitely stand out for me:

1. The fish and chips are Awesome - fillets are delicious, and 3x the size of what I get in the States. The fish and chips are hot, crispy outside, tender inside.
2. Baked goods. Pies, cakes, napoleons, etc are universally fantastic, especially anything made with puff pastry. I got sausage rolls for a pound sixty from under the heat lamps at Tesco that were as good as entrees I've had in US restaurants.