Sit mats

The ground draws heat away much faster than the air, so a few millimetres of foam will retain more heat than a warmer jacket. A foam sit mat is indestructible and doesn't mind rocks, an inflatable one is more comfortable and packs down smaller, while a concertina-folding one is quick to unfold and attach to the outside of a backpack. Choose the thickness according to the season: a thin one is enough for a summer break, while for a winter snack in the freezing cold, take a thicker one. You will appreciate a water-repellent surface on wet grass.