There are several places in Tsinghua where you can eat cash, but it doesn't feel like a long-term solution. Of course, you can overcome this difficulty.
Don't plan the nearest place to eat now, buy a bike yourself. No place to eat in Tsinghua will be more than 10 minutes away from Sanjiao cycling.
Qianqingqing fast food was demolished a few months ago, and now it has moved to the second floor of Taoyuan canteen, which is the canteen in the east of 15 building.
In addition, Yonghe soybean milk on the first floor of the food court (dining hall for ten thousand people) can be used in cash.
The third floor of the Taoliyuan canteen near Building 2 of Bauhinia Apartment is similar to the restaurant outside, and you can order food in cash.
Besides, the Qingqing Noodle Bar on the second floor of Tingtaoyuan Restaurant has all kinds of noodles and set meals, all of which can be paid in cash.