Sandra,
Jo already mentioned it all in a nutshell:
Ramen noodles are available just about anywhere in the world and DEFINITELY do shop at the local markets and stores. Avoid 7/11 type stores or gas stations, the prices there are often outrageous. Grab goodies/sandwiches and such, at the butchers shop, or the bakeries. Keep your eyes peeled to where the young people congregate, be that pizzerias, Kebap or fish & chip stands.
Don't forget that Europeans eat with the seasons and that seasonal fruits and vegetables are always cheap, especially on the farmers markets.
In general, wine, bread, cheese and seasonal foods are the best bargain in Europe.
Check out the food stands, Cafes and Snack places in and around the markets, you'll get good, cheap food of heavenly quality.
Don't be afraid to eat yourself through the market stands either! Ask for samples and bites to taste!
I was horrified at this technique at first: my oldest son, who is forever a student, a world traveler, and habitually broke, is a world champion at this method . .
but I do have to admit that it is fun, AND educational! :-))
Make lunch your main meal of the day - you'll get wonderful meals for an excellent value, just don't be afraid to eat 'Native', because often the daily lunch 'menus' will revolve about the local, seasonal produce/meat/fish/herbs of the day, and you'll get to know the local cuisine in the bargain.
Keep in mind that local, seasonal products are always the best bargain in Europe, and stay far, far away from touristy eateries: if it caters to 'International' tastes, you'll most likely end up with mediocre food at inflated prices!
When in Rome, do as the Romans do! ;-))
With a little savvy, and the willingness to be open to the unknown, you are in for the culinary treats of your life, despite your restricted budget!
Have a ball, Sandra! :-))