We found out that the radio on the truck is not working how else can you hear

You can buy or loan a radio at the drive in. I'm not a 100% sure on the price.

Usually other vehicles around you will be loud enough, we went last night and the car next to us listened through our speakers

You can go inside the concession stand they have maybe 2 dozen seats and play sound in there too

We like to take an mp3 player and connect it to a speaker.

Go inside the concession stand also from everyone else's speakers, it's loud and you can hear