What food items can stay all winter in the cottage and be used the following summer? I know sugar is fine, and most spices.
You’re right about the sugar: If it’s sealed, you can leave it, along with flour, salt, baking soda, soup mix, cocoa, crackers, nuts, pasta, dried beans, popcorn, and other items that contain no water. (Baking powder has a shorter shelf life than baking soda and loses its potency quickly—so get a fresh canister next summer, unless you particularly like flat cakes and muffins.) Items with a very high sugar content—for example, table syrup—or a very high salt content—for example, soy sauce—generally won’t freeze, and are okay to brave the winter cold. All that said, check “best before” dates as you pack up the kitchen. Come May, those stale crackers won’t poison you, but they won’t taste good, either.
As for spices, it’s not unsafe to eat them after they’ve spent a winter in the cottage. But they could lose flavour. The same goes for tea and coffee.
You’ll definitely want to take home anything in glass bottles (which could break if the contents freeze and expand), or any canned food (freezing and expansion could cause tiny splits in the seams, which let air in and spoil the food).
Well, either that or eat up everything before you leave. Get creative! Where else but at the cottage can you whip up a dish using only a can of green beans, half a bag of Doritos, and the last of the ketchup?