Finn and I love playing the drawing game Squiggles. It is a great activity to keep little people busy when waiting at the doctors, on a plane trip or in a cafe. All you need is paper and a pen.
Draw some shapes, zig-zags, or swirls on a page, and the child does the rest. Joining them up, or creating their own drawing from the base shapes.
I always carry a Bic 4 Colour Pen with me so Finn and I can each use a different colour. You can also reverse the roles (let your child do the squiggles you and you create the rest).