Do Not, Wear Denim

Denim is cotton, cotton retains moisture instead of wicking it away like polyester or wool fabrics, once wet, cotton can take a very long time to dry out and given the right conditions will freeze,  any moisture that is held against your skin will be siphoning your body heat away, this will leave you literally shivering in your boots and will render you more susceptible to conditions like hypothermia.

Jeans are not all bad, if your walk is only a local nip up the hill to make room for lunch in the village then thats fine but for the more adventurous....leave the jeans at home.