I grew up in Brighton which is full of cheesy bars like this. If you can handle being surrounded by multiple screens playing Kylie at full volume, its pretty much the cheapest bar in central london. The cliental is so varied its great for people watching and completely un pretentious.
London is blessed with many fine parks, but Brockwell is a real jewel in south London. A short walk or bus ride from Brixton, or right by Herne Hill overground station, the park includes large grassy areas, the fantastic Brockwell Lido (a vast open-air pool – hectic mid-summer unless you get in early - a 7am swim is utterly blissful), tennis courts, a bowling green, a BMX track, a mini-railway, a secret garden, and a few newly landscaped ponds. Perfect for a lazy summer day.
Donlon Books is an atmospheric little bookstore on Broadway Market (in East London.) They sell rare art books, style publications, and homemade photography zines.
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.