I've a friend who was in this same position recently. She put a nice new crisp £50 note in a card for the wee one.
In the past I have bought jewellery as a gift for a Christening, if I remember rightly we bought a single pearl on a gold chain, for her to use when she got older, as a baby would receive all the usual silver bangles and silver piggy banks and so forth, we went for something that she could use when she was older. I did suggest this idea to my friend as a gift for the little girl she was buying for, but she couldn't find any jewellery she thought suitable so she went for the cash option instead