Many supermarkets, pet shops and the local vets supply feed, litter and accessories for cats so there will be no problem there. Just look around and find a supplier (or suppliers) that suit.
I have no personal experience of keeping birds but many people do and there is at least one shop (side of Central Market) that seems to specialise in birds and fish and their necessities. I have also seen bird feed in some of the supermarkets so I am sure you will find what you need.