Customized Linux Stay USB disk with persistence : linux

Hello everybody ! I am a trainer and need to create a customized Stay USB disk with persistence. What I attempted is :

• boot a Linux Mint from Vmplayer ;

• set up Linux Mint on a USB key (from Vmplayer). Now, I might like so as to add some customized software program, and after that save the entire as a straightforward to distribute iso file. How would you do this ? Any software program advice ?

Oh, and I might like the important thing to have persistent storage too…

Thanks !