The AA is Britain's oldest school of architecture, but anyone can take advangte of the great work going on there. You can catch really interesting public lectures and free exhibitions throughout the year. There are also occasional installations and event launches, a bijoux cafe and brilliant bookshop. A great place to hang out with the builders of the future.
St. JOHN is famous for its 'nose to tail' dining which encourages people to eat ‘unusual’ parts of the animal. St. JOHN also have their own bakery and winery and you can just visit for a drink and small bite in the bar (Clerkenwell and Spitalfields).
A short walk from Oxford Circus tube station, Kaffeine is easily one of the best coffee houses in London. Whenever I'm working in the area I pop in beforehand to kick start my day with a well-made cappuccino.