The below is a list of some of your most used stores (physical) in Norway where we get our supplies. Keep in mind almost everything in Norway is more expensive than what you are used to in your country, except perhaps electronics.

Food/Groceries
Most grocery stores are only open Mon-Sat with Sunday closed. However, there are some that have limited opening hours (and space) on Sundays.
Rema1000, Coop OBS/PRIX/Extra/Marked, Meny, Kiwi, Spar, Joker, Matkroken.
Note that freeze dried foods are best found in your sporting good stores, see below.

Gear
The major sporting goods stores are XXL and GMAX. They both have price guarantee so if you find a lower price on a product somewhere else they will match it. And the have, by far, the widest selection on hiking gear. For smaller shops you have Intersport, Platou (very good for the more hiking oriented) and Anton sport.
Online hiking gear can be bought at the abovementioned + Fjellsport, OsloSportslager, HektaPåTur. Note that the Norway Postal Service do not deliver on Saturdays!

Electronics
Elkjøp and Power are the two major electronic stores in Norway. They both have price guarantee so if you find a lower price on a product somewhere else they will match it. You also have NetOnNet which have a good selection. All stores have their own websites so you can order and pick up at the store close to you.