Well...assuming that it wouldn't be the last chance I ever GOT to go to disney world...I would probably go meet Mickey Mouse or another favorite character, like FoulFellow or Baloo. That way I would get that magical encounter, and it would hold me over until I got a chance to plan a REAL WDW vacation!
If it were my last and only chance and I had just 1 half hour...I would probably do what some previous posters said and just walk through the magic kingdom. Right at opening during off-season, mind you! Just to see Main Street, the castle....take in all those little details that the Imagineers worked so hard on to create that magical feeling that in the long run has drawn me in. Get a picture in front of the castle, maybe find one or two hidden mickeys, look at the shops....it would be the best. half hour. ever.