I Think we all the suffer the same in the same situation.
i take my mother shopping I have the PD and she has the old age so its left for me too struggle to put the shopping up on the conveyor, but i try too put like with like so cold stuff goes with eventually cold bag ect in a order that makes sense to me to handle easier and put away easier when we get home.
luckily we now know most of the staff at the supermarket fairly well so, so they know my ways and they know I have pd I always made a point of telling them, so theres no hurrying me at least.
im not too sure about where too get a suitable wallet as most are generic pretty much the same cloth with a motive usually a sport one, you can get those for about 5 quid from sports direct, or there are surfing shops dotted around the country they sell some, with snazzy ozzie esk names on them and designs but they'll cost 15 quid maybe, a shoe/leather shop might have some other designs that hold coins, another option might be amongst the P UK SHOP which is at the top of the page.
this one is located in ipswich might be worth your while looking? i have bought one from here.