And other school fund-raisers. Maybe you can dance, write, cook or play a sport. Sharing whatever you're good at is a great way to volunteer your time at school. They want to know how hospitals, factories, businesses, government agencies and other organizations are run. You can help teach Caring, Respect, Hard Work, and Patience.
Quality is much more important than quantity.
Look into public transportation. Talk to teachers and other school officials about these and other options. Many businesses allow time for employees to volunteer in schools. Another possibility is to host a class field trip at your place of work. Some parents have health conditions and are unable to volunteer at school.