Balance board by Byclex
 
Improve your balance before getting on bike. 
 
3 options available. 
 
Some ideas:

Wobble forward and backward or side to side.
Try with your eyes closed.
Stand on one leg. (carefully!)
Balance a book on your head while wobbling.
Play catch with someone while standing on the wobble board.
Time yourself to see how long you can keep your balance without an edge touching the floor.
Pushups? 
Squats? 
 

Made of 15mm thick birch plywood
Roller has rubber bands to save your floor
Board with engraved arrows for better grip
Stoppers at each end of the board won't let you fall down. 
Eassy assembly, quick change of options.