One of the very popular cafes in Wellington uses flat smooth stones with the order number painted on it - they are so popular that they now sell them as so many were taken home as souvenirs 
 
 
Another cafe I have been to uses plastic animals - so your order might be the elephant or zebra or cow rather than the boring #5 

 If you could find some at a second hand shop it might not be to pricey
good luck - it sounds like a very good idea 
