Just to spit-ball a simple idea mob drops like how chickens can do eggs (and on another data pack feathers)
Pigs: Clay ball, beetroot/potato/carrot [pigs are messy eaters]
Cows: flowers, and loose grass
Horses/Donkeys/Mules: wheat seeds, flowers
Parrots: feathers, melon & coco seeds (maybe other topical items)
Cats/Ocelots: dead bats, feathers, string (that way village cats are useful without taming)
Phantoms: membranes, fish
Bats: gun powder (very rare), coal?
Pandas: bamboo
Polar bears: salmon
Wolves: rotted meat & bones? (arguable from throwing up a previous meal)
I'm sure there are some better ideas/options but would change up the game a bit.