If you don't have a card, you have to pay 20% tax, which is about 840. It doesn't matter.
There are three restaurants: Xueyuan, Xiyuan and Sanhaowu (foreign student restaurant), all of which are very good and taste good.
If you want to rent a card, you can rent it at Tongji BBS and see if anyone rents it for free. Generally, students at school have to use it for themselves, which is inconvenient to rent.