[header] How to keep your posture straight when you carry a heavy backpack [title] Wear the backpack as it was designed to be worn. [step] Namely, wear it on your back, with all parts doing what they're supposed to do. [title] Wear both straps. 
[step] Place a strap over each arm so that the straps sit evenly across each shoulder. Wearing the bag on only one shoulder causes strain and will make your posture lopsided.