If you like some nice cool beer, portuguese sweets (the once with yellow custard inside) tasty and affordable sandwiches, good strong coffee and football, at all hours. Max Snack Bar is worth checking out.
A brilliant little hidden gem of a place to relax and look at some interesting rare / Out of print books and Magazine. Their evening art events are also very special. Great atmosphere and great people.
A great place to start the day if you are in South London is Federation Coffee in Brixton Village. The food is great and so is the coffee. This is a very chilled place where you can get both and indoor and outdoor experience (even though the whole place is under the Village roof).