What are ways to get cheap groceries?

I’m an international student in Kristiansand and I’m looking for ways to safe some money on groceries.

I normally shop at KIWI or REMA 1000 and I’m also using the discounts they offer, but sometimes I wish my fridge was a bit fuller than it is now.

Besides that I noticed that TooGoodToGo is a thing here, which is why I’m using it 2-3 times a week.

Is there anything else I could do/ be on the lookout for?

Tusen takk!