Students can have their lunch in any student cafeteria and canteens ("menza") of Charles University for a discounted price. The list of Charles University cafeterias is available at the Dormitories and Refectories website.
If you would like a specific meal, it is better to reserve your lunch a day in advance (till 4:00 PM). To be able to use the online ordering meal service, you are expected to charge your student card at the cash desk. Each meal will then be charged from the cash you have deposited at the cash desk. You may also use your credit to pay for other food at the cafeteria (small snacks, pastries, coffee etc.).
The new Faculty building in Troja (Patkova 2137/5) has its own cafeteria where you can buy small snacks, sandwiches, coffee, and other refreshments.
There is also a University canteen near the Faculty building which is located in one of the dormitory buildings (Patkova 3) right next to the Faculty building. Currrently, the canteen is closed because due to reconstruction but it is expected to open during October/November 2020.