This would make a fun Halloween theme science experiment. Use some spooky, Halloween colors for your food color. Orange. Black. Dark green. Red (blood).
You’re going to start with your jar (or in our case an old glass candle jar) half-filled with vinegar, with a few drops of color added to it. Squeeze in some dish soap, give it a stir.
Now add a heaping spoonful of baking soda.
The dish soap makes it bubble rather than the quick fizz. A nice volcano eruption. It is not a quick erupt and done but lasts for a few minutes.