I love couches. They are so comfortable, welcoming, and accommodating to my relatively short legs. I even love Anantasana, which is sometimes translated to "Vishnu's couch". So, it only makes sense that I would use my couches for yoga props. In fact, even before I owned a single blanket, I was backbending over my couch.
When you are staying with a friend, and you've foolishly left all your yoga props at home, you can still get many poses in by using their couch.
Side note: do not do this off the back of the couch, couches are not stable that way.
Couches are reassuringly soft and are great props to use when you attempt dropbacks.
To round off your practice, it's nice to end with a supported shoulderstand / viparita karani hybrid. Take one cushion off the couch and place it under your shoulders. My couches were just high enough off the ground to wedge the cushion under - perfect support and I could move the cushion in or out.