UK based Valley Kayaks make a nylon emergency shelter called the Igloo that fits into a pocket, yet can cover up to four people and drastically cut wind chill. During a surf kayak class with kayaker Nigel Foster years ago, Nigel for fun put us in one of these at lunch on a blistery day. The inside temp increased dramatically and became rather warm. The yellow glow inside was fun too. The Igloo is so small that it could fit in your fanny pack or deck bag while out paddling.