MY favorite engagement sessions are when the two of you go on a date and I tag-along. Will I interject myself into the date and set-up photos? Absolutely. But as you are already in a place of your choosing, where you feel comfortable, the having-your-picture- taken-for-an-hour thing is less stressful.
Accessories: I love it when clients bring items that can create a quick visual change without too much stress: things like scarves, hats, jackets, glasses, sweaters work well.