Stickers are a great way to decorate things with Sonic. Good on binders, notebooks and more...and also inexpensive to collect. Here are 2 sticker sheets from around the time of Sonic Adventure 1. The left set is Okee Dokee (known for stickers and tattoos) and features just about all the Sonic stock art they could get including 2 Skii Sonics (which are uncommon because he didnt ever actually skii in that game) Skateboard Sonic and DJ Sonic. The disk you can recognize from what ReSaurus used in their packaging.
The other set only has the fine-print but gives you one for all the main characters, including 2 neutral chaos. Notice that it says "Dr Robotnik" and not "Eggman" because the issue was still being messed around with at this point.