Do you regularly drive for work without proper reimbursement?
Does your job require that you regularly drive, yet your employer neither reimburses you for your gas not provides you with a company vehicle? Does your employer refuse to pay you for your time when you are driving, even though it's part of your work? If you're paying out of pocket for gas, the vehicle and insurance, and driving somewhere as required by your employer, your employer may be taking advantage of you.
It's likely that your employer is violating your rights and employment laws by doing so. Under federal law, excepting the commute from home to work and back again, travel you engage in as required by your employer should be considered paid, working time. Driving for work gets considered work, and your employer should pay you the same wage for time spent driving that they pay for when you're at a desk or work station.
Driving for work is part of your job
If you are driving, other than your commute, it should be considered part of your work day. Many employers try to sneak around this requirement, but doing so is possibly a violation of law. It can be easy to overlook or ignore this kind of issue. After all, you may think, it's only fifteen minutes a day to drive from the office to the shipping center and back. Doing it without complaint makes you look good to your boss, and it may even feel like a little break from the stress of work each day.
The problem is that those little amounts of time add up, as does the wear and tear on your vehicle and the gas usage. A fifteen minute trip every day for five days a week, 52 weeks a year results in 65 unpaid hours of work! That's more than a week and a half of pay you've been denied by unfair employment practices. Depending on your gas mileage, that could be many hours of pay in gas as well. You deserve to get compensated for any work you do for your employer, even if it is just running packages in to a shipping company.
Start documenting your time and expenses
Make records of the time you spend driving when you aren't getting paid. Record mileage too, so you can prove how much gas you've used. As time wears on, it will become clear that you are losing out on wages and spending your own money for gasoline. Attempting to address it with your manager may be a wise first step, if you think your manager will be sympathetic. If not, you may want to review other options for getting the reimbursement for your time that you are owed.