I've actually hosted 2 Noah's Ark themed showers.
~ If you can find animal cookie cutters to cut out sandwiches those are very cute, as are bowls of animal crackers and cookies on the tables.
~ Make cupcakes and top them with animal or rainbow picks.
~ Go to a candy making supply store (or Michael's) and purchase candy molds in shapes of animals or teddy bears and candy melts. Make candy animals in colors to coordinate with the nursery or invitations.
~ For one of the parties I decorated the cake with a Noah's Ark mini tea set (and gave it as a gift to the mom to display in the baby's room) and curled ribbon in colors to match.
~ For fun give your food and drinks "animal" names...we do this with all our parties regardless of the theme, and place name tags in front of the plates, platters and bowls. For instance, at our Harry Potter birthday party we did Harry's Hogwart's Hot Dogs, Ron's Chocolate Frogs, Severus Snape's Snowcones, Hedwig the Owl Suckers (in owl shapes,) etc., so your imagination is the limit : )
~ We don't play games anymore because people find them too boring, but have a tip suggestion where everyone submits a tip to the new mom and she picks the one she likes best and that person gets a prize. That could be a small basket of decorated animal sugar cookies from a local bakery.
~ For party favors a box of animal crackers with ribbon tied to the string.