Disney is very particular (and rightfully so) about people following the rules when it comes to FastPass+ reservations and tickets.
So, we totally understand when people want to be cautious about being sure that they abide by all the policies that Disney has in place. But what about when you have a traveling companion that decides they don't want to ride something? Can somebody else use their FastPass+ reservation?
The truth is that as long as that person has entered the park, you definitely CAN borrow their MagicBand or ticket so that you can use their FastPass+ reservation.
Sometimes you may find that you're not feeling like taking a spin on Space Mountain or maybe you decide you don't want to get wet on Kali River Rapids - but you have somebody in your party that would LOVE to ride it twice. They can simply take your MagicBand or ticket and scan it just like it was theirs and then hop on the ride.
Now, if you are planning on doing that you'll want to make sure that your bands or tickets are clearly labeled so you which one belongs to each person, but outside of that you should be good to go!