DIY spring-back chop sticks could be used to work on fine motor skills and coordination for kids. You can use them with food, small item manipulation activities, or any other task that requires fine motor coordination.
Could also connect a bunch of locks and put all the keys on a key ring. Lots of pictures of latch, lock, etc ideas for montessori type preschool. This lock one could be made with 2 boards, some o-rings, and some locks from Dollar Store.