A very quick, simple and frugal art project M and I did the other day when I just couldn't think of anything else to do (after we role-played Honey Cake Mixup story 10 times in a row).
All it takes is an ice-cube tray and food coloring. Oh, and of course some water. Pour, mix colors, freeze, then paint with colorful ice-cubes. And they look utterly delicious too. Actually, M ended up eating a couple of them after cubes melted down to a more managable size.
The result was very messy and cold, but after drying looked like watercolors. And believe it or not, this arts-science-sensory-fine motor skills activity kept M occupied for a whole half an hour!