When in the flexigrid list view, I thought it would be nice to have "All" as one of the options in the items_per_page drop-down.
Here's how I did it by hacking one line of code in list_template.php.
In config/grocery_crud.php add an option of a million items per page, for example:
Then around line 139 of assets/grocery_crud/themes/flexigrid/views/list_template.php change
It's not elegant, but it adds just a bit more functionality to GC.