I have to give these guys a mention. If you love a good book or are a music fan, you must check them out. They have a huge selection of both for give-away prices. They have a good selection of clothing and housewares as well (my better half, last week, purchased a good-as-new, £450 Diane Von Furstenberg dress for just £30!). And Oxfam really do do some wonderful work around the world - They are worthy of support.
Not to forget of course they are always looking for donations (just nothing electrical which they are not allowed to sell as they do not have an electrician to check appliances are safe for sale). Instead of throwing everything in the bin to end up in a land-fill somewhere, stick it in a bag and drop it off in the shop at the corner of Kingsland Road and Forest Road (just 2 mins from the square).