If you are thinking of eating at restaurants every day you should have a quite loosebudget because it will be very expensive, in addition, mostly European restaurants can be really expensive. It is best to use the existing supermarkets. It is pretty cheap to buy some bread or canned food (sardines, tuna, salads). The first few days it will cost a bit since you still have in your memory the food from home, others say that it is difficult at the end of the trip since eating bread and canned food during the entire trip is not pleasant!Sure, every once in a while, it feels good to have a little better meal. Well, for that you have McDonalds (McDonalds is like God is everywhere!) " trash food"/fast food will be a true delicacy in certain circumstances. In some countries like Croatia or Hungary the "menu" is relatively cheap the but the same is not true for France or Austria, for example, there is not worth eating at fast -foods.
In most places in Europe the water is potable. Thus, one can only survive without buying bottled water, except for two situations: either you may want fresh water, or it may be necessary to renew the stock of bottles because current ones may be broken . At the arrival in each city I suggest that you inform yourself about the quality of tap water because often can even be better than bottled! Remember, bottled water can be very very expensive in warmer countries.