A stylish flap over case!
This is likely to be a breif-case style school bag...but it is quite stylish! It has a nearly 80s asthetic, with the radiating lines & choice of font for the Sonic word. It has a seldom-used but quite nice looking pose for stock Sonic, & the addition of leaping Tails there in the background is nice. It's also very 'segasonic', with the yellow sideways logo & it being reiterated in the fonts below him. It looks like it buckles shut, has a single handle on the top & is likely made of nylon canvas and maybe faux-leather?
This is quite a nice bag, and it looks like it is thick/quality with the stitching and textures you can see here.