The best thing about any charity shop is that you never know what you are going to find. I have a well tested route around London that includes all of my favourite charity shops. This Oxfam has a great selection of books and often turns up some interesting clothes too.
In terms of materials and form, these galleries offer so much. On an abstract and typographic level, so useful. This is a section of an altar frieze, from the Eye Temple at Tell Brak (N.E. Syria), dated 3300–3000BC. The Egyptian rooms take the tourist weight; these spaces are much quieter and amenable time spent drawing and thinking.
This is one of my favourite places in the whole of London.
Cernamic, run by Nam and Susi, they offer some fantastic workshops and at a very affordable price. They have really cultivated a welcoming environment, full of lovely people and a place to share and recieve knowledge.