You cannot use Google Play credit to buy hardware (like Pixel phones, Nest thermostats, or Fitbit trackers) from the Google Store.
You can supplement your balance by answering short surveys in the Google Opinion Rewards app , which pays out in Play Store credit.
A monthly subscription that gives you access to hundreds of premium games and apps without ads or in-app purchases.
It is important to note the limitations to avoid "locking" your money into the ecosystem: