What should I do with the remaining fuel coupons allocated to me, which were not used to transport me to and from home, and should I return them to the company?

The crucial factor lies in the terms and conditions of the company that arranges for the payment of tickets for employees. If the company pays for the tickets for the employee and does not demand the remaining amount back, then there is no harm in benefiting from what is left over. However, if the company provides it for the employee to use only for their work-related needs, and any excess beyond that must be returned to the company, then the employee must return the remaining amount to the competent authority, according to the established system, in order to clear their responsibility.