The disposable camera idea was great.
Also, consider:
- extra batteries and memory card if you're bringing a digital camera
- baby powder (if it's hot) or a small sprayer of her favorite perfume (to feel refreshed as the day goes on)
- Disney dollars
- extra socks, bandaids, moleskin to keep away the blisters
- an index card or small sheet with your ADR confirmations or other key info.
Have fun!