How to Choose a Backpack: The Complete Buying Guide for College, Office and Travel Knowing how to choose a backpack saves you from the most common buying mistake: picking a bag because it looks good online, then finding out it hurts your shoulders, cannot fit your laptop, or struggles through a rainy commute. A backpack you carry for hours every day is closer to gear than an accessory, so it needs to suit your body, your load and your routine.