When I was at Roskilde Festival I had been carrying either a heavy backpack or a rucksack for a week, and I got a terrible pain in my back, shoulders and neck, and I found that these two Yoga postures really helped to ease up the pain.
Uttasana Shoulder stretch
Stand in an upright position.
Place your hands on your lower back and intertwine your fingers.
Bend forward and let your hands fall down toward your head.
Standning Neck Strech
Stand in and upright position
Intertwine your fingers and place them on the back of your head
Let your chin drop down towards your chest.