Just a simple tip, which can safe you money.
I hear quite often that people think that eating at a restaurant can be expensive when visiting Stockholm. I agree, add a beer or 2, and you can quite easily increase the bill at the end of the night.
A simple solution: eat a hot lunch at a restaurant and go for budget food during the evening (buy bread, sandwiches, whatever).
In Stockholm it is extremely common to go out to a restaurant for lunch when you are at work. Most restaurants serve on work days something called ‘Dagens rätt/Dagens lunch’ (the daily dish, look for signs outside), and most of them offer 2 or 3 of them. You pay somewhere in the range of 50 to 90 SEK for a full hot meal, most of the time including a drink (water, light beer, soda), bread, a salad and coffee. That way you can easily save some money, which in turn can make your stay in Stockholm more enjoyable.