Ooh how fun! I love empty jars and bottles.
-I think it would be fun to store/share all sorts of glitter or specialty glues/paints/ink.
-For a more practical purpose, you could save a sample of all the wall paint in your house and have mini "touch up" bottles.
-You could paint the inside and make them into teeny tiny vases!
-Or! You could paint the outside of them and stick them on a string of christmas lights! I think it would be cute to paint them like little jack-o-laterns and string them on lights for a neat glow effect.
-I saw an idea on pinterest the other day where you mix colored chalk with salt (just stir a chalk stick in a small bowl of salt) and it looks like colored sand. You could do mini sand-art with kiddos!
- Are they glass? You could do some simple glass-cutting and cut off the neck of the bottle. Then maybe make small candle votive out of them - even with the leftover stuff stuck to the bottoms of nice/expensive candles that never burns!
-They could be neat spice jars.
Hmm... now I want a bunch of tiny jars.