What are some fun things to bring to a concert?

It's my best friend's birthday in a few days and I think it would be
fun to buy her some little things that would be fun to have at the
Maroon 5 and Train concert we are going to in September but I don't
know what to get her! I can only think of glow sticks. I don't want it
to be too expensive cause I am buying her ticket.

Thanks for your ideas!!