You can find lots of street food at traditional shopping streets.
- Nakamise Dori Shotengai (Shopping Street)
The shopping street from the gate of Sensoji Temple to Sensoji in Asakusa. Probably the most famous shopping street for tourists. You can find, croquette, melon pan, soft serve, age-manju, rice crackers, etc.
- Sugamo Jizo Dori Shotengai
The place is located in Sugamo, near Ikebukuro. It is also called as "grandmother's Harajuku" as it gathers many shops for older generations. You can find many delicious food in here, too. Japanese sweets (dango), melon pan, croquette, an-pan (bread with red bean paste), eetc.
- Sunamachi Ginza Shotengai (Shopping Street)
Sunamachi Ginza is located in Koto-ku, which is in the east side of Tokyo. Among the three, Sunamachi Ginza Shotengai is the most non-touristic shopping street. The atmosphere is very local and you can surely discover great food here. I recommend trying Yakitori sticks and Menchikatsu (fried meat ball with panko batter), and a can of beer here!