What part does a harmonica play in a band?

So, I wanted to start a band, and I got a bunch of friends and everyone brought their instruments over and I tried to work everything out. We currently have a 2 Guitarists, Bass Guitarist, Vocals, and Me, on the Harmonica. So I figured, the guitarists can just be Lead and Rhythm, the Bass will play Bass, and the Vocals with of course sing. My question is, what does the harmonica play? Not a lot songs have a harmonica part so I don't know what I would be playing. I used to play with a ukelele player and I'd play the vocals on my harp but the band doesn't need me to play vocals. So, don't know. I heard some play the horn part in a song. What do you guys think? (It's kind of selfish but, I do want to be in the band, I did find, and get everyone together. And Transporting and stuff. Yeah. I also bought the burgers and shakes.)