Less is more. Props overpower a newborn so very fast. One prop at a time and hopefully something tasteful and simple. The hats. bows and flowers are "in" but I promise you that when you look at your images in a few years you'll say "WHAT was I thinking?" So use them sparingly and carefully.
blankets and things to swaddle baby in are awesome. Textures to lay baby on such as the fuzzy fur are nice.
Newborn images should be about life in it's purest form. I find my best props actually come from the parents. Things that mean something to them or the family. Silver rattle or bank, a blanket made by a grand parent, etc.
On a sick note... I had one family ask to have portraits done of the great grand daughter in the dress that the grandmother's niece DIED in. Don't be shocked by anything that they ask you to do... people are a strange strange breed.