If taste isn’t a concern, I’ve gotten by with chlorella and cocoa chia pudding for longer than I care to admit. I don’t mind the taste of chlorella, but most people apparently don’t find it and other seaweed all that appetizing, but it’s a drink so you can just chug it like a beer or something and neutralize the taste with like a splash of lemon juice or water with lemon juice. Won’t fill your stomach all that much, though.
Miso soup (with wakame and maybe tofu and veggies cut down to tiny pieces?) is also a great addition to that.