Are you planning to go to cottage then shop, or shop en route?
If go to the cottage first, I would take tea, coffee, biscuits etc so you have something on arrival, and milk at service station near destination. Then I would look at cottage to see what was needed.
If shopping en route, I would buy enough food for first 24 hours.
From home, I would take tea towels (there’s never enough),, plus sone cheap hangers which I would probably leave there.
Also, if dc has a particular favourite brand of cereal, biscuit, squash etc, I would take that with me.
Also, not sure when you are going but start saving £2 coins. Then you’ll always have car parking money available.