No, Why would you keep the money? Only irresponsible people would pick up the money off of the ground, put it in their pocket and leave. Now for example  if  you’re walking around the park and you see a penny, a dime, or even a $1 bill that’s ok as long as you didn’t see someone drop it,  then you can take it. Even if that $100 bill and your money put together would get you a decent bike doesn’t mean that you should be selfish and spend it on yourself. You should report it to the Police Department that you found that wad of cash on the ground and see if anyone has claimed that it’s theirs. Would you rather have a clean heart and NO guilt, or would you rather be a thief and feel guilty for maybe the rest of your life and be convinced that the person would be MAD at them for stealing their money.