I use these blank jigsaw puzzles in schools and hospitals with young people as well as at home with my kids, and they are great for making alternative birthday cards that the recipient has to assemble before being able to read!
They are available in packs of 10 or so online and job local craft stores.
Doodle with felt tips, use stencils and stickers.
The activity time is lengthened as the finished artwork then becomes an activity to break apart and out back together!