I’m for bricks. Theres, like, a kajillion in the Great Pyramids and the Great Wall of China alone. And if you count Lego bricks in that number, I’m sure it goes even higher.
And another question: are we going according to quantity or mass? I could see how buttons win over bricks in sheer numbers, but bricks would be a lot more on a scale.
Dust? Its mainly human skin, or so I’ve heard.
Carbon dioxide molecules?
I’m with flodnak. Legos. Also crayons. A lot of folks are posting objects that are already trash - hamburger wrappers, diapers, cans, etc. I say LEGOS.
Or AOL cds. We’re thinking of building a studio in the back yard to enshrine them all. 
My first thought was cigarette butts.
Crap.
Half-assed opinions.
How about pages. Or sheets of paper. Lots of those around.
Coffee cans? You always see zillions of those. If you look in my apt, you would think beer bottles.
Beer and soda cans. They turn up in the woods, miles and miles from civilization. It used to be pop tops, but they stopped making cans with those.
I disagree. There’s only one Spoons, and he’s a member of this board. 
Teeth.
Not counting the ones that grow in our mouths and are still there in lots of skeletons, but teeth on combs and on gears and all those little wheels you find on bicycles and inside printers, and most anything with moving parts. Plus all the teeth in the dentures that we make to replace the teeth we have lost.
Automobile tires. Yes, there are more nails, but tires make up lots more bulk.
Plastics? Say, the kind that they make playgrounds (and everything else) out of? This stuff takes forever to decompose, lots longer than bricks or nails, and has so many applications.
Hey! I resemble that remark!
As for the OP, I like the choices of nails and buttons. I’ll also add wheels–not just those on wagon and cars and bikes, but also wheels in machinery, cog wheels, gear wheels, any round and flat object designed to turn around its centre.
well for sheer volume I have to go with concrete/blacktop/asphalt, I mean that shit is everywhere.
what about wire? speaker wire, telephone wire, all that wire adds up.
but nails is definitly very close to the top of the list if not at the top, if you just call it metal fasteners and lump staples and screws with nails you have a winner for sure.
Wax Paper
Carpet fibers. There must be a billion individual fibers in my house alone.
Chinese people. 1.4 billion and counting. . .
Single shoes in the middle of the road.
How does that happen anyway?
condoms