My mom and step-dad feed their dog rice when she's sick. Seems to help.
Rice can be a bit rough on some dogs... Potatoes, maybe? I knew this dog once with a horribly sensitive system, and he lived on potatoes and white fish.
a little pepto bismal....youll have to look up doesing online.
Watch for dehydration by monitoring fluid intake and gums. If the gums are dry, the dog might be getting dehydrated. I learned this the hard way when one of mine got colitis and had to stay overnight for fluid resusitation. She immediately felt better after getting some fluid.
Good luck. Rice is indeed a gentle food, as is scrambled eggs which my vet suggested. (Obviously no good for vegans.)