We've done2 surprises, one we had a scavenger hunt (actually a hidden mickey hunt - dh made mickey heads out of wood and painted black) that led to a big disney box, inside we're disney $, pennies and quarters, new wdw for kids book, etc -- and a note that we were leaving in 17 days. We did this on Christmas. I told them ahead, so they could have fun in planning, etc.
The second time we did disney, then the cruise and then I surprized them with another 2 days back at WDW. We got in the towncar from Port Canaveral and I had told them we had a LONG day of travel home, with a layover in Atlanta for 3 hours, etc. Instead the driver took us to the Cont. The driver knew our secret, DH told him while they put the luggage in the car. Girls never paid attention, sitting in the back seat, and we got all the way to the WALT DISNEY WORLD entrance sign. Then the driver said, oh, no - I've gone the wrong way.....the girls looked up and they the driver said guess I have to take you back to the Cont. It was cool and the driver had fun.
If you are having a towncar pick up, the driver could hold a sign that says: Lisa and Ed, you're going to Dinsey.
Have fun!