I use links to reward tables for cooperative behavior. This helps when you are trying to get children to follow directions quickly (like, take out your math notebook) or to work independently for extended periods of time.
The only thing about this system is - sometimes children get upset when one person in the table isn't doing the right thing. But, on the bright side, you can take this as an opportunity to teach social skills. "Instead of being upset or getting angry at someone, how can we help our friends make better choices?" Soon enough, you see children quietly tapping their friends and calmly reminding them what to do.
Once a table accumulates 10 links, the children at the table get to pick a prize from the treasure chest. The best part? One person from the table takes the links home. It's such a big deal to them!