Best...
Art supplies, we have a whole room with everything you could ever want and if the kids don't use it then I will so no chance of wastage. It is our most popular room.
Loose parts; recyclables, blocks, rocks, shells, gems, odds and ends, anything that can be manipulated and rearranged in an open ended fashion. We were also gifted speilgaben which fits into that category in our house and gets a lot of use.
Light table. Brilliant. Mirrors go well with one or with anything.
Trampoline.
Lego, wooden train set, wooden marble run - classics.
Animal figurines (and pokemon). Very popular.
Dress ups.
Doll house.
Instruments.
Board games.
Books.

Waste
Can't really think of anything we have currently but we had a junk when they were babies. Gifts. Your typical loud, flashy plastic with an expected singular use.