Some simple ideas to try

At times these actions seem so simple they feel dumb, but here is a list of ideas:

• Unplug your phone and DSL router if you're going away for a long weekend (we just did this).
• Make sure your car's tires are properly inflated. Better still, use Nitrogen rather than aire, as it will last longer before needing to be topped off.
• Seek out non-stop flights. Most of the fuel is burned during take-off, so avoid stopovers (for a bunch of reasons!). Tip: JetBlue now has a non-stop from San Jose to Boston.
• When you're too busy at work to eat at the cafeteria, why use a cardboard takeout box? Consider taking your lunch back to your desk on a plate and returning it the following day. Ask for some tin foil if you think you'll want to keep some leftovers for later. Re-use the tin foil. I did this last week, though admittedly I felt rather strange driving around with a ketchup-covered plate on my passenger's seat!
• Buy biodegradable bags e.g. Biobags Thanks to Corinna for this tip. They make everything from kitchen and bathroom bags to poop bags for your dog. Arf!
  
• Check craigslist.com for free stuff before going out and buying something.
• Also, consider shopping at Salvation Army, etc, for generic things like kitchen odds and ends.