How to make a bootable USB flash drive that performs certain actions on startup?

Question

Boot disk

It is necessary to implement the following task.
I insert a USB flash drive, boot from it, pre-defined actions are performed (for example, copying files from a hard drive to this USB flash drive, launching programs lying on a USB flash drive), after working out the system turns off.
As far as I understand, the easiest way to do this is by modifying some linux livecd, setting it to autorun a script that performs all the necessary actions and shuts down the system.
But I don't have knowledge on choosing, configuring and modifying linux livecd.
I ask you to help me choose a way to implement this task, as well as help me figure out the rest of the points. (It would not be superfluous to link to instructions for the implementation of the main subtasks).