Fill it with sand. Secure the ends and lay it across the bottom of the door. Caulking is always a good energy saver. Check around your light fixtures for holes to fill with caulk. Window panes that have cracked sealer around them can also be caulked.
Electric blankets are a hugh source of wasted energy.
Drippy faucets can waste up to 15 gallons of water a day when a washer to fix one cost pennies. When using a dishwasher always air dry your dishes. Taking showers instead of baths can save 13 to 18 gallons of water. Using over head fans for cooling can save big bucks on your energy bills. Most can be reversed to use during the colder months as well.