Shop at antique stores, holiday bazaars and thrift shops. Someone's trash may be someone else's treasure. Consolidate purchases into one bag. Better yet, bring along a few from home and reuse them. Reuse packaging cartons and shippings materials.
Old newspaper makes for excellent packing, too.
Shred some at work and bring it home, if you can. Save fancier bags and use them as gift wrap. Paper grocery bags can be used to wrap small to medium sized packages for mailing. Walk to local parties, or carpool if you have to drive. Run appliances such as the dishwasher, washing machine or dryer only when full.