What is the ruling on the remaining money left by an employee for the gas delivery collector, in exchange for cutting the line?

Your friend's leaving the remaining amount of money to the employee in exchange for cutting the queue is an obvious bribe and an illicit gain (suht) consumed by the employee, and it is impermissible for either of you to do that. Furthermore, his mediation in bypassing people and completing your transaction before them without a valid sharia (definition)-compliant excuse or their permission is not permissible, and it falls under the category of an evil intercession (shafa'a sayyi'a). You both must seek forgiveness from Allah (istighfar), repent, and not return to such actions.