These tips from the American Academy of Orthopaedic Surgeons and American Occupational Therapy Association can help you avoid neck and shoulder pain from your bag:
See Avoid Back Injury with the Right Lifting Techniques
Limit bag weight to 10% of your total body weight. For example, a person weighing 150 pounds should not carry a bag heavier than 15 pounds.
Choose bags that are worn across the shoulder, messenger-bag style. These are the best at distributing the weight more equally.
Do a “bag purge” once a month. Bags tend to accumulate extra things that don’t need to be carried around all the time. Weed out the items you’re not using, are done with, or are duplicated.
Use more than one bag, depending on function. Use a smaller purse when you’re running an errand or two and save the full-size purse for trips or all-day excursions.
Switch arms often, so one elbow or shoulder is not bearing the weight all the time.
Choose a bag with compartments, so the heaviest items can be stored low and evenly.
Choose a bag with wide, adjustable straps. Narrow straps concentrate the weight on a smaller area.
Choose travel-size options for lotions, make-up, or hand sanitizer.
Remove extra cards and loose change from your wallet.
For more information on how to prevent pain from heavy bags and/or purses read this article from Spine-Health.com