A rather interesting reaction that you can do is to add vinegar to baking soda. It should fizz! The fizzing is carbon dioxide being produced.
Another reaction involves swirly patterns in milk. What you need is a mint tic tac. Pour some milk into a large plate. Put some food colouring in, drop the tic tac in, and it should fizz. If you drop some detergent into the milk it will swirl.
