Do you mention gifts when you send out invites? Examples... no gifts or do you ask for specific gifts/donations/guidelines, etc?

We never mention gifts with our invites but maybe I will in the future. I usually recommend books or send an Amazon wish list link if anyone asks for ideas when they RSVP. I've seen a range of requests included with invites...no gifts, no plastic toys, books only, specific charitable contributions, contributions for college funds, no boxed gifts, etc!