Why not see if family or friends could use up the left over materials for a project of their own?
If you are renovating an old house or replacing old fittings with new (e.g. baths, sinks, radiators, fireplaces, mouldings, Georgian panel doors, wooden flooring, old lights) contact an architectural salvage yard that buys and sells pre 1930's furnishings:
Holyrood Architectural Salvage Yard: T: 0131 661 9305, W: www.holyroodarchitecturalsalvage.com.
East Lothian Council Architectural Salvage Store: T: 01620 827 474. Accepts donations of items such as listed above.
Alternatively find your local Community Recycling Centre for a list of recyclable DIY materials.
The Edinburgh Scrap Store is a project promoting creative reuse by collecting and distributing unwanted scraps including tiles, wood and art materials. You can also become a member through their website and use any of the resources stored at the facility!
T: 07870621086; W: http://www.edinburghscrapstore.org.uk/
Reduce the purchase of DIY tools by using the Tool Library - a place for people to share tools and equipment.
If buying new timber fittings look out for the FSC (Forest Stewardship Council) label indicating timber from sustainably managed forests. Suppliers of FSC wood products include B&Q, Co-op, Habitat, Homebase and IKEA.