Baby Shower Gifts

Hello, I’m throwing a baby shower for my sister, this will be her first baby. She’s registered at Baby’s R Us, but I also wanted to let people know that it’s OK to give hand me down items, since new items can be so expensive. I also don’t want it to look like we’re just fishing for gifts. Any recommendations on how to word any of this? Should I just alert people when the RSVP and not mention any registries or gift suggestions on the invitation? Thank you.