Hehe this is funny, I had exactly this problem with carrying around all of my textbooks in a carrier bag, (not so good in the snow and rain!) and my mum had the same idea as you - of buying a satchel. I'd never thought of it but my mum got me one from Tom Brown's Satchels, she chose brown and it is just the perfect size in a 15" for carrying all of my books, notes and also fits my laptop and charger in. I just had a look at the Cambridge Satchel company (never heard of them before) and their satchels are more expensive than Tom Brown's, a 15" costs £104 from Cambridge but only £81 from Tom Brown's and the quality on my satchel is beautiful, so I think I'd recommend them rather than Cambridge! Hope that you're all having a happy Easter. Marine and freshwater biology sounds amazing by the way! I can imagine you having an amazing career diving and spending your time in the great barrier reef! C x