The closest you can get to Little Italy in the east.
The owners are amazing, the atmosphere is relaxed, the lunches are abundant and homemade.
The cakes are amazing, try Torta Clara (pear and chocolate) for the ultimate bliss.
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.
I've only just discovered this fantastic little salad bar-come-florist right round corner from my studio. It serves freshly made salads that are not only delicious but cheap too! Either take away, or grab the one and only table and eat in.
Quinto sells second-hand books. I spend a lot of time here and have found some inspiring books over the years, both at Quinto and the other shops on this road. Koenig Books on the corner is good for art books, too.