The Clover point of sale system has a very easy to use offline mode that will give you the ability to accept credit cards even when your device is offline. Once you have enabled the offline mode, the Clover system is smart enough to kick over into offline mode the moment your internet connection is lost. You can take a look at the settings for this within the Setup app.
When you open the Setup app, look for the “Payments” tab. Towards the bottom of the list, you should see “offline payments’. You can tap this button to adjust these settings. You can enable/disable the feature, as well as put per transaction dollar limits, offline total limits, and you can even require an approval before accepting the offline transaction.