The brick?
And I see someone’s beaten me to “the club.” (Better “beaten to” than “beaten by,” at least.)
That’s easy. The Pet Rock. 
More seriously, earthenware bowls would be a good bet.
Also, walking sticks. The wooden kind.
Cabers might be good, but I’m not sure how old caber tossing is. But that seems like cheating.
Bear skin rugs would of course work, but I’m not sure they’re really “manufactured.”
Chalk would probably not be too big a surprise, aside from how regular it was in shape.
And all sorts of gold and silver jewelry would fit in fine.
And toothpicks! Can’t forget those.
And 45 rpm record players. What? Those are totally ancient.
forgot whips.
I’m going to throw in musical instruments of the primitive type:
Flutes
Drums
Fiddles, guitars, lutes, harps, shamisen, koto, sitar, type stuff
Horns
Rattles
Gongs
Moog synthesizers 
Anyway, something in the category probably can be found wherever they find calculators and art works.
Pez.
Only the head changes.
The space shuttle?
Extreme laughter!
Dice again. Do these count?
I’m surprised axes haven’t been mentioned. You need them to cut lumber and they also make nice weapons.
“For oldest and unchanged” it’s hard to think of anything more versatile than a stick with a hard object secured to the end. With minute modifications in size, length, weight, flatness/concaveness and sharpness of the hard object, this becomes everything from a spoon to a shovel to pickaxe to a hammer to an oar to a mace.
The dildo.
I think unglazed pottery would beat nearly everything mentioned. It’s older than anything but stone tools like spears, hand scrapers, and the like. And, unlike those stone tools, continues to be used to this day. While clubs or spears would be the earliest human technology, modern versions are much less similar to the primitive versions than is the case with pottery.
the human.
they’re composed of essentially the same things they always have been, and the manufacturing techniques are pretty unchanged, if anything they’ve gotten cruder
The ball point pen has been around for quite a little while.
But I really like cement, invented by the Romans!
buttons haven’t changed at all.
[Caveman]Hey, look what Zog do![/Caveman]
a bicycle
I actually like the “dildo” answer – “materials” used in contemporary dildos would tend to startle.
I’d imagine books is a good answer, specifically a mass-market paperback copy of the King’s James Bible.
Eyeglasses.
Most glassware used for drinking/cooking.
Fishing nets.