On way is to have a hidden form open when the database opens, and that form should set the values of all public variables right from the start.  You can make an Autoexec macro to open this form in hidden mode, and this form should have VBA code in the Open event that sets the public variables' values.  Database-wide public vars should be declared in a stand-alone module, of course.  If you don't use this method, you'll have to put this VBA code in every form, every report, etc., everywhere that uses the public variables, which is a lot more work.

If the value never changes you can use a global  constant or System Defaults.