I have several children currently on my caseload who perseverate on topics like, "I need to go to the bathroom" or "I want some water," to avoid completing tasks. This token system is used to remind the child how many opportunities they have to repeat the same phrase. Once they have run out of tokens, they can no longer mention or ask that question. If they do, there is a consequence (i.e. no computer time or what ever highly preferred activity they have).
I recommend printing and laminating this token chart to keep it sturdy and using the blue speech bubbles as manipulatives that can be added and removed using velcro pieces.