At this late date there isnt much you can do and I wouldn't worry if I were you. It's a little to late to register, if you already haven't. Just put inside the invitation a list of things the baby needs and have them shop from that. You can also ask them to attach a gift receipt to the gift, that way if you receive more than one of something, or something you don't want, you can exchange it for something else. For food, you can ask your guest to bring a dish or you and your friend can make finger sandwhiches, get some chips and nuts, make a cake or buy a cake and then that's done. You can always find a list of baby shower games on the internet and some don't require props, like "how many words can you make out of the words baby bhower" or "guess the size of mommy's belly" simple thing like that.
Don't stress. If you think simple, you'll be fine.