Coffee - lots of good places along Nevsky (the main street) and all around the city center. Coffee is usually rather strong. I personally love the coffee shop on the second floor of Zinger House (or Book House – major book store in St.Pete) – you will find this impressive building easily in the very center of the city. Perfect coffee, good pastries and snacks and the best view on Nevsky prospect and Kazansky church. Definitely worth a stop.
I also like the chain called Shokoladnitsa (chocolate girl). I believe they served the best hot chocolate in the city. And good coffee as well.
Vegetarian food. Almostevery restaurant or café has a vegetarian option. For example many people like to have quick lunch in Teremok – Russian fast food café serving blinies with different fillings. So you can have it with mushrooms, cheese, fish and so on.
Idiot on Moika is a very good place – very friendly.
I like Teplo restaurant -yes, it is not vegetarian but fish and vegetables are offered.
There are two Indian restaurant 2 min awat from the Hermitage museum – Tandoor and Tandoori nights.
Try also the café called “Troitsky most’ (Trinity Bridge). It’s a chain so choose the one on your way:
Kronversky prospect, 35
Or Malaya Posadskaya 9/2,
Or Vasilyevsky Ostrov, 6th Line 15
or Vasilyevsky Ostrov, 6th Line 27
Or Bolshoy prospect, 55
Or Grand Cafe "Troitsky Most"
Zagorodny prospect, 38
Have a pleasant trip!