Mrs Growster's sister used to have to buy Paxo stuffing over here, and smuggle it in to the US...
Paxo - while not a sandwich condiment - is an additional must for roast pork or chicken!
Mrs Growster's parents ran a fabulous small pub in Rye, back in the 'sixties, and she would provide a 'Club Sandwich' for 2/6 (12.5p now)!
It was three slices of toast, filled with bacon, fried egg and tomato, and they went like hot cakes! When the pub was busy, she had to pop back into the kitchen to form the sandwich, and we all had to muck in serving drinks until she got back!