I have a non Bluetooth car. Is there something I can buy to play MP3's off a USB flash drive?

Yes there are gadgets that plug into the lighter socket and transmit a FM signal to the car radio. IMHO they work, sort of. Look at:

https://www.amazon.co.uk/s?k=car+fm+transmitters&c...

Some of these only take SD card, some SD and USB

Yes, there is something you can buy to play mp3's off a flash drive. Lookit: https://www.amazon.com/Bluetooth-Transmitter-Anguo...

**************************************************************************************************************************

I would not do it that way, since phones can be loaded with mp3 and transmit through AUX cords, bluetooth , cassette adapters, or mp3 on CD can carry more than 8 hours of program per disk.

Several questions need to be answered before anyone can answer this for you. Only thing we have is Non-Bluetooth and that you don't have a CD Player. So what is the deck currently? Someone suggested FM tuner. Got 3 down votes. What kind of budget and how good do you want this to work? What car do you have? Do you want bluetooth ability or just USB?

If budget is of no consequence, just upgrade the car stereo head unit with something that gives you a USB input. There are many brands with USB inputs. I personally have a couple of Kenwood units that have USB inputs. And the deck can be had for under $100. Should give you decent quality sound based on your MP3 recordings.

And most current decks should have USB and Bluetooth capability as well. Also Aux input on some of those decks as well.

You should just burn the mp3 songs to a CD