Babyshower..HELP?

My 2 sisters are throwing my baby shower. Mainly my older one..she already bought decorations and we are going to go get more things tomorrow. But what I want to know is if when someone throws you a baby shower do you help money wise too? I don't have a problem helping and I told her I can but she hasn't asked for money. But I don't want to come off as if I don't want to help. This is my 3rd baby and the first two my aunt and mom did my shower and I was young and a teen mom. They surprised me. But now I'm older and can help so I don't mind doing it but really don't know how it works? Am I suppose to buy food and decorations too?