Store session data after successful login

Use session helper.

My problem is not how to set the session variables, but where. After a bit of reading it seems the easiest solution would be to set the session data in the 'successful login' event?

The successful login event seems reasonable yes... in fact I'd probably say that's the "right" way to do it. Implement a listener and add your session data in the handle method...

namespace App\Listeners;

use Illuminate\Auth\Events\Login;

class PopulateSession
{

    public function handle(Login $login)
    {
    // Populate your extra session data here
    }

}