Here's some ideas I've seen in other threads (sorry I can't remember who the credit goes to...):
-- Waving "hello" to the castle (or hat or tree, etc.), taken from the front
-- Waving "goodbye" on your last day, taken from the back
-- Kids or parents and kids walking down Main Street hand in hand taken from the front and the back
-- Ask the photopass person to turn around and take the photo from the other angle (i.e. with the train station behind you instead of the castle)
-- Sit on the bench (or curb, or stand next to the lightpost, whatever) next to the photopass person, they will take it from that angle
-- Jump for joy
-- Ask the balloon seller to let you (or your older child) hold the balloon strings (they will still hold on too) and have them take that photo. It can turn out really cool
-- Take a before shot on your first day all excited and happy, then an after shot on your last day, exhausted or "crying"
-- Always ask for the magic shot they have available
-- Tell them you have preordered the CD and tell them to snap away
-- Tell them you really enjoy candid shots as well as posed shots
That's all I can remember right now. I'm sure the other threads are out there. Maybe someone can link to them.
