Listening in car

I recently got a new car with a pretty good audio system and USB input.  I want to use a memory stick/flash drive to give me access to many musical options.  What's the easiest and least expensive to load music onto a memory stick?  I have a Windows PC but, when I go to the music folder, there's not much.  I have lots of CDs (now in storage because I now use an Innuous Zenith). Is there a way to transfer the CDs I  previously burned onto the Zenith hard disk to a memory stick (I actually tried using  a USB  drive in my car made from the backup feature on the Zenith but my car would not recognize it).  I can load some CDs onto my PC (which does have a disc drive) and then transfer them to the memory stick but it's time consuming and my stored CDs aren't very accessible.