If you've got more than one device, if you've bought a new device or if you have done a full reinstall on your current device it is possible to restore your in-app purchases on a fresh copy of the game.
Purchases should automatically update upon installing onto a subsequent device from Google Play. In the event that they do not, simply make sure you are logged into the same account which was used for purchasing the items in question, then select [Restore Transactions] from the bottom bar of the Store menu page. Wait a few moments - your transactions should then be restored.
Edited by Neil Brock