New York: Engagement Photos

Also, while we are in New York, my dad has offered to shoot our engagement pictures for us (photography is a hobby of his).  I'm very excited and have a tentative list of locations:

• Sage (where I went to college at)/downtown Troy - they have some gorgeous brownstones 
• The Playground - where Dave and I spent time together before we started dating
• Prospect Park - a nice little park that we went to frequently 

I need to keep this in mind and get some ideas:  What to wear for engagement pictures!

Though he's agreed to go along with it, my fiancé doesn't really get the purpose of engagement photos.  I am planning on using them for Save the Dates, Invitations, and possibly in the guest book.  If you're having some done, what are you using yours for?