I buy the huge bulk cans of dehydrated veggies that they sell for disaster food storage. I write the open date on the label with a permanent pen, and DH and I use leftovers to enrich soups all winter. I also put small amounts of leftover veggies into freezer bags, and when they get full, I squeeze all the air out, and freeze. When I make soup it is never the same twice, so it doesn't get boring. I also buy powdered milk for cooking since it is cheaper and lasts longer on the shelf.
Instant potatoes, dried diced potatoes, powdered milk, dehydrated onions, a couple pats of butter, and you have a great start on homemade potato soup.