If you fly intro Tromsø and plan on road tripping all the way down to Lofoten, you'll definitely want to stock up on supplies, since this is the biggest city you'll be in the whole trip.
That said, who wants to waste all their time running errands when you're so excited to be here?
This shopping center not far from Tromsø airport is a convenient one-stop shop for a supply run, since there's a grocery store, an outdoor store, clothing stores, etc., all under a single roof.
Pick up anything you might have forgotten (or didn't want to pack as luggage), and it doesn't even require going in to central Tromsø , which you don't want to do with the campervan anyway, since clearance on the tunnels might not be high enough for your van.