Here’s the thing – most of the food products you have mentioned with have changed. Manufacturers produce what sells – taking into account government and consumer demands. So with the move to natural flavours and colours, reduced salt, lower fat, lower sugar, vegetarian / vegan demands etc most products have changed significantly from the 1990 to now, let alone the 1970s.
Hence most will be worse – and generally a lot smaller, than you remember them
However things that are worse:-
Monty Python ( and most comedy) has aged badly
Blakes 7
Star Trek
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