Is it permissible to use a flash drive allocated for personal work before its renewal date, knowing that it renews automatically and the organization pays a fixed bill, and it is not possible to obtain permission from the manager?

The employee is entrusted with their work and tools, and it is not permissible for them to use them for purposes other than work without explicit or customary permission. If using the surplus balance does not affect the tool or harm the work, then it appears there is no objection to it, and it is something that is customarily overlooked. It is preferable to seek permission from the official or their representative to avoid any doubt.