豆花 (Dou Hua, or Flower Tofu) comes in both high and low end versions. This snack restaurant has the mid range, with little bowls of soft tender tofu in a starchy sauce and all kinds of great things on top. Below is 馓子豆花, san zi dou hua - the crumbles on top are 'san zi'.
The 牛肉豆花 (beef dou hua) is great as well.
You can get many Chengdu signature snacks here. They do a really good beef 粉蒸肉 (meat steamed in rice meal), one of the more expensive things on the menu board but very worth it. I particularly like their shui jiao (little, very tender pork dumplings in a sweet garlic and hot pepper oil). The tian shui mian (thick, chewy noodles in a dark sauce that is more sweet than spicy) are good too. Shui jiao:
The 口蘑面 (mushroom noodles) and 担担面 (dan dan noodles) are less great. 小谭豆花 is an institution and has little seating, so during busy times you might find yourself standing behind someone's chair waiting for them to vacate it before you can sit down. Address: 西大街86附13号