What am I?

I scream for attention at all times. Some people would say I am pretty bright, but I can be pretty empty at times. One thing you should know for certain is that I will always have your back and I am here to help. Depending on what I put in myself for the day, I can weigh a whole lot or be pretty light weight. I get occasional compliments for my looks. I would have to agree that I definitely draw a lot of looks my way. I'm pretty durable and I can take a beating. I don't usually mind the rain, or even the snow for that matter. At times it is difficult to keep my mouth zipped but I never make a noise. I usually hold a lot of information inside of myself at one time, but it comes and goes. I get thrown around a lot and usually don't ever get to ride shot gun, but I know I am appreciated. I am almost always convenient to have around and lessen the loads that bear down on people's lives. You would think by my (brand) name I would be sporty, but I am actually more on the nerdy side. I love long walks and good books the most.