I think a box full of glue, paper and collage items (buttons, beads, pom pom balls, foam pieces, etc) would be a great idea. It takes controlled movements to use the glue, pick up the small collage items and place them on paper. Those really help with muscle strength and control. My 2 year old in just a period of a few weeks is getting better at grasping and picking up the items for her collage.
If you have a 40% off Michaels coupon they have a great arts and crafts jar filled to the top with goodies for $9.99 that you can get for $6. Then you can add a bottle glue ($1), construction paper ($2) and possibly a Crayola Craft Surprise box ($12).
I really love the Crayola Craft box. It comes in a plastic storage container (think shoe box). It is filled to the top with many items. My DDs last box included: stick glue, 16 Crayola Crayons, 24 Crayola color pencils, 2 paint brushes, 4 small bags of air dry clay, scissors, coloring book, small Crayola Wonder coloring book with 3 Marker, plastic toys to use with Play Doh or clay, white drawing pad, 2 travel size boxes of crayons and color pencils, water color paints, 6 mini pots of washable paint, color your own stickers, 2 paint sponges and 3 tubes of glitter glue.
If you use the coupon. You could set up a really nice craft box for about $20.
You could also get a kid size balance ball.
Jen