Never accept plastic bags in stores (always use your own cloth bags). Buy beverages, yoghurt, etc. in large containers instead of individual portions. Compost your kitchen waste. Re-use containers. Don't print everything you read on your computer. Get your bills online instead of in paper format.
Volunteer?? I am not sure how that fits into the eco-friendly picture, unless you're volunteering at a recycling depot.
Hope this helps:)