Answer: The token should be an item that cannot be used outside the token economy.
Step-by-step explanation:
A token economy uses the theory of applied behavior analysis to reinforce desired change by rewarding positive behavior. The rewards or tokens should be valuable to the person who needs a behavioural change but also easy to introduce and remove, as well as limited to the system. It should not count as currency outside the token system. This is to limit the motivation for collecting the tokens to behavioral improvement alone and prevent dependency.
Also it is ideal to have a target behavior that needs changing, instead of 10, as is the case in this question. A single target behavior is easy to monitor.