While it's easy to buy paint, it's sometimes nice to have an 'edible' paint, something that your child can get on them, and their clothes and it doesn't make a difference.
There are loads of options for home made paint, and as many recipes, but basically it's pretty simple: flour, water and food colouring.
Different recipes call for corn flour or plain flour and specific quantities of water, but in reality, there are no rules! I had self-raising flour in the house, so I used that. I also didn't use a cup measure, instead just adding water till it got to a consistency that looked 'paintable'.
From there, pour the flour water mixture into different pots - I used muffin trays - and add different food colourings for different colours. This was quite fun as I used one drop of red, three drops of red, one drop of green, four drops of green, one drop blue, two drops blue and one drop blue and red together, and left one white.
I'm not all that brave with paint related clean-up, so my girls often end up painting in the bath ;)
We have a long roll of paper from ELC* which I just tear from as needed, and this particular art activity became wrapping paper for a birthday present.
It does dry slightly brittle, and isn't likely to be the kind of wrapping paper you'd reuse, but it was pretty anyway, especially since as it dries, it darkens.