You can seal any plastic bag by placing a piece of aluminum foil over the end to be sealed and running a hot iron over the foil. Make sure you have foil on both sides of the plastic to be sealed so it doesn't stick to the ironing surface. No expensive sealing gadget required.
Plant shrubs and trees so that they will shade your house during summer months. Doing this will help you to not use your fans and air conditioning as much, hence saving on your electric bill.