Engagement Photos Outfit Change

So we are doing our engagement photos this Sunday (FINALLY -- we booked our photographer in December last year but we have been engaged for 2 and a half years so far and needless to say this is a long time coming and I want to send out STDs ASAP). I have 2 outfits that I want to wear, a floor-length dress and a sweater with jeans and boots. My question is: if you have done 2 outfits during your engagement shoot, when did you change outfits and where? FH is so confused as to where I am going to make this change, probably in the car? Should I ask my photographer what she thinks or what she has had people do in the past? We're doing the photos on a cute little street and then further off the street is a historical site with old buildings and a creek, so we won't be in the same place for the entire time and I don't think I could carry a bag or anything because I don't want that in our pictures.