It may not have been the best of summers so far but here's hoping for a glorious, Indian summer. In which case you'll need one of these.
This is a totally practical version made from 100% polyester fleece with a water-proof PVC backing, so you can stretch out with impunity.
It also, conveniently, folds into its own carrying case.
Size: (L x W x H) 1420 x 1170mm