Trust me, don't bring protein powder to add to the soup. A single meal without protein isn't gonna kill ya. Potato soup, french onion soup.. something along those lines will work well. Even ordering a sweet potato can work, just take tiny bites and keep it in your mouth until it's nice and smooth/runny.
Do try and avoid anything like chicken noodle soup. It's soft, but those noodles... (maybe it's just me, but I can't handle noodles even now, and I'm 3.5 months out). Even the broth has noodle juice in it.. so doesn't work for me. YMMV