Give the wallet to the bus driver and hope that he can locate the owner. Take the wallet home and create a Facebook page dedicated to said wallet in hopes that it'll go viral and the rightful owner will claim it. Try to locate the owner by searching the wallet for a driver's licence or some other form of identification. If you are unsuccessful, you keep the wallet. Do everything you can to locate the owner of the wallet. If you can't find him/her, you donate the $100 to your favorite charity.