A small bottle full of planet mini globes.
Mini MercuryMini VenusMini EarthMini MarsMini JupiterMini Saturn Mini UranusMini NeptuneAnd Mini Pluto
The planets use relative, logarithmic-like scaling to each other.
If an object is smaller than another, it is probably a lot smaller, and if it is bigger, it is probably a lot bigger.
(Jupiter, to "proper" scale with that Earth, would be near the size of a watermelon!)