Here's a new backpack in 2017 from Spencers' Gifts.
It's all-Sonic all the time with this school bag! In black & white square tiles all over the bag are various expressions/poses of Boom Sonic. They're not CG, but rather solid colored art of him. (Most boom things use only CG, so that makes this bag a little unusual)
It's a fairly standard bag with shoulder straps, large main area and flat/pop out front zipper pocket. It is probably around 30 or so dollars in store and should be online too. Yes, that is the "Sonic the tombstone" poorly shaped bag above it in the left side photo.