I have just logged in and seen your question has not been answered yet, so sorry about the delay.
Regarding his meds - none of them absolutely have to go with food, so you can try them given directly orally. I would focus on getting the zantac syrup down as your priority as that can help with the nausea. If you can get that to stay down for 30-60 mins it may help. Then try the noroclav tablets, but don't worry too much about the prokolin at the moment. If you can get the meds to stay down, then try him with some food - but a very small amount, may be one or two mouthfuls. The fact he is drinking is a good sign, as it will help him keep hydrated, but we need to make sure the fluid is staying down as well
Things that would make me want to see him more urgently than monday:
1) Inability to keep oral meds down
2) Inability to keep water down
3) If you pick up some loose skin at the base of his neck, pull it away from his body and then release it, it should sink straight back down. If this does not happen or it sinks slowly, then he could be dehydrated.#
If he is being very sick still, your vet may want to repeat the cerenia injection as it is potent anti-emetic, and if he is dehydrated he may need fluids. With the weather we are having at the moment, dehydration is likely to occur more quickly than it might in cooler weather.
I hope this is helpful to you, and if you have further questions when you come back online then please do not hesitate to ask.