My dog is being sick / diarrhoea. Any advice please?

My dog is being sick and has diarrhoea. This started just over twelve hours ago.

I have an appointment with the vet later today, but wondered if I should give her something myself to stop the vomiting/diarrhoea?

Should I give her some food or starve her until she has seen the vet?

Is there anything I could give her myself without having to see the vet?

I also have another dog. They have both been fed the same food, and the other dog is OK.