I would add a couple of things. If you like art museums, consider taking the S-train to the stop for the Louisiana museum. It's on the coast, north of Copenhagen - lovely museum and sculpture garden, lovely setting. Can't remember the name of the station, but information at the Central Station in Copenhagen can point you in the right direction. The museum has a good cafeteria, where you can get coffee or a light meal.

It may be a bit of a splurge if you are doing a super low-budget trip, but I would suggest taking one of the coastal boats (the Hurtigruten) between Bergen and Trondheim. Boats leave every day from every port on the line, and there are a number of options for tickets, I think.

Julie