Clean out your purse, backpack or briefcase on a regular basis. Depending on the size and how often you use the item, you may need to clean it out weekly. It is easy to accumulate unnecessary items over time. The less weight you carry, the more healthy your back will be.
Buy a bag, purse or backpack with a long strap that can be worn on the opposite shoulder as the item. This allows the weight of the bag to be distributed more evenly across both sides of your body. It also helps keep the shoulders aligned, which helps keep your back from injury.
For severe back pain, see a physical therapist. Consult your doctor and if he or she thinks it is a good idea, they can probably recommend a great one for you. A physical therapist can teach you exercises and techniques to help you deal with your particular type of back pain.