Grey tote bag with Celtic knot keychain found

I found a grey canvas tote bag this afternoon around 2:30pm, lying on the benches in Princes Street Gardens by the Waverley tram stop. It's about 12 by 14 inches, with a faint coffee stain on the front pocket and a blue striped lining that you can see when you open it. Inside there's a small notebook titled Edinburgh Sketchbook and a blue Celtic knot keychain clipped to the zipper. The bag looks used but intact; it seems important to someone and I’d love to get it back to its owner.