Put VAT on bottled and canned drinks and use the money to install drinking water fountains and get rid of standing charges on tap water.
Make energy companies pay to allow anyone to make their home energy systems controlled by internet/smart phone.
Increase air passenger duty on any journey that can be completed by train, and use the money to reduce the cost of train travel. This would also help solve London's airport capacity problem by reducing short haul flights.
Make it illegal for hotels to switch the air conditioning on in hotel rooms before the guest has arrived.