Checkout File Locations

Checkout application is located in /Applications
Store (name is: Database.checkout): [Checkout User] Home/Library/Application Support/Checkout¹
Crash Log (Crashlog): [Checkout User] Home/Library/Application Support/Checkout/crashlogs
Report Templates: /Applications/Checkout/Contents/Resources/Templates²

The Checkout User is the Mac User ID that installed (and maintains) Checkout.
To get access to the Contents folder, click on the Checkout application icon while holding the Control key on the keyboard. Select Show Package Contents in the small pop-up window. In the resultant Finder window, select the desired folder(s).