I have no idea how much money I need for the three month trip across Norway with a bicycle. I know I will have to eat a lot of carbohydrates, rice, spaghetti, and sometimes meat, fish.. I will make soups and pancakes..I will have pots and stove with me, I will do most of the time wild camping, now and then I will go to hostel and camping place to wash. so how much money is enough per day, let's say, two meals a day? 10 Eur? 15? 20? Thanks for help :)
I can't really tell you how much money you need..
but I can give you some price examples:
rice, 700g, 32kr
spaghetti, 500g, 10kr
potatoes, pr kg ~8kr
apples, pr kg, 9-13kr
tomatoes, pr kg, 20kr
You can get flour for your pancakes really cheap, oatmeal really cheap, some types of vegetables..
Kiwi (a food store chain) normally has a weekend offer where they each friday sell one type of meat or fish quite cheap.
Here is a link for you.. I know it is all in norwegian, but the tables list prices of different normal products in different food store chains. Maybe this can give you an idea of prices.
http://www.dinside.no/836389/rema-1000-slaar-kraftig-tilbake

Carbohydrate staples are relatively inexpensive. You can also get cans of tuna for relatively cheap, for the times you need extra protein and you don't find fresh fish or meat that you like.
When you're cycling, look out for farms and the such that sell their produce to visitors. You can get good fresh fruit and vegetables and maybe cheese/meat for good prices...

Quite difficult to set an exact budget since you're quite flexible with cooking your own meals, camping etc.
For grocery shopping I would stick to the food store Kiwi or Rema 1000 as they tend to be the cheaper ones. As # 1 says Kiwi has weekend offers with different types of meats and fish going for 15 nok. One piece might not serve for an intire meal but it's a good start. Norway is expensive so if you can get by on 10 eur pr. day I would call it a revelusion :) I think you need at least 20 eur. Perhaps 30, but it's quite difficult to set anything exact.

OP - if you're planning on eating simple and "spartan" meals, then 10-20 Euro a day shouldn't be a problem. You may want to treat yourself to some of the freeze dried camping food (I don't remember the brand name offhand; the package is orange) once in a while. It's expensive - 60-70 kroner per package, but there's a lot of food in it (about 600-700 calories worth). The "steinbit" casserole is especially tasty :-)