The information below seems to be about Germany!!!!!!!!
Since Germany uses the Euro as a main currency there is not much to exchange. But if you need to exchange money, it is always better (cheaper) to bring foreign currency into the country, than to exchange it before you leave.
There are lots of "Wechselstuben" (Exchange booths) scattered all around the city, most of them -of course- near the Hauptbahnhof (main rail station) and the other big stations (Altona, Harburg, etc), and the airport.
As a general rule: The further north you travel, the cheaper your daily life also becomes. Expect to pay 6-15€ for a meal at a restaurant, depending on what you eat, drinks etc. not included.
There are lots of small "fast food" stores that sell Döner, burgers, fried sausages with fries etc. Most of them do not franchise though, so you won't find exactly the same menus everywhere. But you can get a decent lunch for 4€ at e.g. a take-away indian or chinese place.
In general, food is cheaper in Germany than e.g. in France (especially the big cities), but not quite as cheap as e.g. in Greece or (I'm told) Italy.
Watch out: The Ladenschlussgesetz mandates that most shops (supermarkets and malls) have to close at 8pm and may not open on Sundays. If you need something to eat at night or on Sundays, you can go to any gas station, they usually carry a fair amount of general-purpose food too, but are more expensive. If you can, always go to a discount supermarket (Aldi, Minimal, Lidl, Penny, etc).