We used some old pillowcases for sack races in the backyard. We did several heats since the kids were much faster than I thought! We also played "musical pillows", which is just like musical chairs except you jump on a pillow when the music stops.
For the birthday kid: Fill each balloon with a dollar bill before blowing up, hang from ceiling for a surprise when they wake up. The best part is getting to POP them and watching the dollars fall from the sky!