My favourite way to stretch out my lower back (I do this all the time):
Stand with your feet hip/shoulder width apart. Keep your back straight and reach forward. Without bending your knees, keep reaching forward and stretch your arms downwards, try touch your twos with your fingers, or if you're really flexible, hands flat on the floor. Let your head hang. Hold for ten seconds. Bend your knees and slowly roll yourself back up, bringing your head back up and straight last (to not put strain on your neck).