Depending how he has kept these organizing and cataloging the coins and notes is a good first step. The good news is it doesn't have to cost a lot, there is a lot of information online and you can enter the details you find on a spreadsheet with things like country of origin, type, mintage, and other information.
As said don't clean anything and if you can find some way to protect or organize them this is much better than having them thrown in a jar knocking against each other.