How will you be cooking your food? I'd recommend a small Trangia or equivalent portable stove, you can buy fuel (alcohol) for it in most grocery stores in Sweden. If you get a gas stove, you can find canisters in camping supply stores. The right to roam doesn't always include a right to build a fire and it is not uncommon for there to be wide bans on making a fire during the summer due to dry conditions, while stoves are usually ok.
You should be able to buy cheap canned food at Lidl-stores.