To stretch the shoulders, armpits, triceps and chest at the same time, you can do the Gomukasana (Cow Face) arm pose. Just stretch your right arm up, rotate it inwardly so your thumb turns downward towards the floor. Sweep your arm down and behind your back, bend your elbow and bring your hand in-between your shoulder blades.
Inhale and stretch the left arm up with the palm tuned back, bend the elbow and reach down toward your hand, and if you can, hook your fingers together. Roll your shoulders out and feel the stretch in your chest and upper arms.
Usually this arm stretch is done sitting down, but you can also ad it while doing Warrior One for variation.
Info from Yoga Journal.