That singing fish animatronic. Convinced people it’s a god. Wait for the battery to die and the eventual religious crisis.

Bicycles. If we could have gotten bicycles a few centuries before cars, I don't think modern cities would be so damn car centric.

A snow globe from Niagra Falls, a clothes hanger, A Buttplug, a die cast Model of The General Lee, some Tide pods, an assortment of Weeble Wobble’s, The Complete Jane Fonda Workout (large print, hardback edition), A magnifying glass, A bag of Candy Corn.

A solar panel with a light attached.

Something with gears. Like a cranked egg whisk. Huge amounts of science went into this, but all of it should be replicable in a few generations of experiment with even bronze working. And it should inspire inventors of the age too

A single glass coca-cola bottle

I would take a portable CD player, place a CD with Rick Astley's Never Gonna Give You Up on it playing backwards, hook up solar panels, remove the ability to shut it on/off, and set it up a circuit that will:

• As the device solar charges, keep it off until some voltage threshold is exceeded
• Once the voltage is high enough, start a random timer (8 - 100 hours), so that it is not immediately obvious that the sun activated the device
• When the timer ends, turn the music on on repeat mode
• Sometimes turn the music off at random, and then turn it on again at random after a long delay, so that in some cases you can have turn 'ON' events without the device being exposed to the sun
• When the voltage drops below a low threshold, turn the device off until it is charged again

A large obsidian slab standing perfectly vertically.

If you’re looking for the biggest change in our timeline for the littlest work I’d give a hindu-arabic numerals to early Greek mathematicians. Watching those guys try to wrap their heads around zero, that would fuck Pythagoras.

oh I'd teach 'em modern english, and then dump a truck load of People's Magazine's outside their hut

Going for a hunt today? Can't. Need to know what Janniston said to Branjelo on page 4

A bicycle.

A Nintendo Switch running Animal Crossing. Assume it has some kind of perpetual battery, and they can figure out how to operate it/play the game, and read our modern English.

I'm thinking they figure modern civilisation is about (or back to) fishing and farming... and that animals are intelligent. Like validating TF outta the Egyptian pantheon. You're a human but you have a dog for a neighbor, here's a koala, a gorilla, an eagle... and they all talk and wear clothes.

(Of course, if we wanna blow their minds with a game AND we can assume they can play it, why not just go straight to Cyberpunk?)

A monolith

One of those 3D printed non-round gear toys. They could immediately appreciate both the impressive technology that went into designing and manufacturing it, and that it has no use whatsoever. Which would be a trip.

Magnets

Leaf blower. They are loud and the "breath" coming from them is pretty awesome.

A Furby.

One of those pens from bawdy seaside resorts where you press the button on the end and the lady's clothes disappear. Might as well be magic.

Flashlights.

i would give them nuclear weapons

A Roman dodecahedron, it fucks with modern people as well.

I'd just give a LGM-118A Peacekeeper MIRV to the Aztecs and say nothing more. I wonder if they would eventually manage to do something with it.

Condoms

one of those fleshlight vibrators that suck your dick

a slot machine and a battery to keep it running

A bottle with a highly concentrated solution of polonium, radium, plutonium or anything spicy and ionizing.

Preferably coupled with something that glows nicely, like ZnS. Just pick a suitable fluorescent dye and make it blue or green for bonus points.