I PSM'd a production of Ragtime a couple of years ago. One of the biggest things we had was sound. There were not enough body mics available, so we had to do a pack change during intermission! Also, the two sound designers were there at each performance live mixing. We also had 6 mics backstage that the actors gathered around to sing when they were offstage to bolster the vocal quality.
Another fun thing was Coalhouse's car. We had rented one from a props company that was designed for stage use-aka, quiet, smaller, easy to operate, etc. However, it was stalled more often than it worked, so we had to attach fishing line to the back of it and create a pull system to get it onstage and offstage if it did not work.
Like in previous posts, it really depends on the vision of the designer and director as far as how complex the show will be. Good luck to your production!