Some cheap and healthy things: Oat meal, beans, tea / water, fruits of the season, yoghurt, rice, pasta, potatoes, sweet potatoes, cabbage.

I can easily imagine eating for around 2 Euro a day or even less. It just would not be as much fun. So I get around with 5 to 7 Euro, that allows me to add delicious ham and some other meat to my diet in small portions.