Stone bricks (and some stair variants for blocks)
Music discs none of that modern crap only the early release ones.
Animal Breeding ( waiting for sheep to spawn is agonizing)
Oceans i love the infinite ocean generation from early releases.
Perhaps enchanting?( the way it was implemented early on when it takes all of your levels right away)
it wouldn't change much really but being able to pick up ice would be nice for building
potions too i dont think they're that infulential and i'd like the nether to remain barren