What should I do to make my dog comfortable?

My dog was laying down for about 15 minutes just chewing his nylabone like he always does. All of the sudden he starts heaving and throws up. He kept trying to push something out with his mouth partially open and his eyes were moving around. His vomit was light brown and kind of had the consistency of wet sand, but when you put it between your fingers it crumbled. It didn't have any unrecognizable objects in it. He kept making the noise of a dry heave, but he didn't have anything left to throw up. His back was arched and he was shaking. I had him chew on an ice cube which seemed to help and lightly rubbed his throat, back and stomach, then gave him a little brown rice and chicken (which he gobbled up). He went to the bathroom (pooped and peed) but occasionally makes the heaving noise. I have an anti-nausea medication that the vet prescribed to him on another occasion (Cerenia) and endosorb (for previous diarrhea) but I didn't think I should give him those in case he ate something and it needs to get out of his system. Is there anything else I can do for him? I'm going to take him to the vet tomorrow (he's due for his annual next week anyway), but is there anything that I can do to help him now?