|Advocate - the most obvious soution is to talk to friends, family and colleagues about these things. If you can persuade two friends to halve their car usage and only buy local produce, you've probably done more than you could ever manage yourself to reduce C02 emissions. Try persuading your employer to switch your workplace to green electricity, for example.
Campaign - get involved with your local Greenpeace or Friends of the Earth group (UK-specific links, search the web for groups local to you). Remember what public demand did to GM food in supermarkets. Voice loudly your concerns!
Use your voice and write to your MP about these issues.
Keep informed about environmental issues and sustainability. Find out about local or global action and get involved. Improving your local environment is part of improving your community spirit. Have a look at the Evergreen newsletter.
Support and join charities and NGOs (Non-Governmental Organisations) that are working towards Sustainable Development and fighting for our futures.
Boycott companies and their products that put profits before people and planet. Use your power as a consumer. www.ethicalconsumer.org and www.greenpeace.org.uk have extensive lists of companies and products we can boycott.
Having many different shoes, the coolest car and latest mobile phone model will not be of much use if we have no air to breathe, water to drink or crops to reap...