Stockholm is a beautiful city and there is much to do. Don’t miss the Vasa museum (a wonderful museum), the Stadshuset (City hall where the Nobel dinner is held … make sure to take an English tour as the guides are excellent), and Skansen (the open air museum). Gamla Stan (the old town) is also nice. You can also visit Drottningholm either by taking the boat or a combination of subway and bus. The gardens are beautiful and there is an interesting theatre from the 1700s on the grounds. Uppsala is a good day trip (about 45 minutes from Stockholm by train). It is a university town with a large cathedral. If the weather is nice, you could also take a boat to one of the islands on the archipelago. Another nice day trip is Gripsholm Slott in Mariefred.
Östermalms Saluhallen (www.ostermalmshallen.se)is an indoor food market that sells produce, cheeses, baked goods, etc. It is a great place to pick up things for a picnic and there are also a couple of places in the market where you can eat. You will see lots of traditional Swedish foods. There are other food markets at Hötorget and in Södermalm, but I think the one in Östermalm is the most impressive and traditional.
Another place that I love for lunch is Rosendals Trädgårdscafe www.rosendalstradgard.se. This is an apple orchard and garden on Djurgården (the island in Stockholm where Skansen and the Vasa museum are) which has a wonderful café that makes excellent sandwiches, salads, and baked goods. It is very Swedish … sit outside at picnic tables in the orchard.