Drink milk,I've heard it has a small nuetrulizing effect,and eat the basic absorbing foods...Bread,crackers,ect...Then to be safe,get a ride to the E.R...
I remember when I first took hydrocodone, I got clammy, shaky and had cold sweats. I for some reason thought milk would help. I researched after and apparently milk is good. I usually drink milk as a comfort drink whenever im nervous so I guess I got lucky. He should be fine just keep pumping liquids into him. If he passes out id go to the hospital
Caffeine? I was always under the impression that if you're vitals are slowing down caffeine could stimulate them enough to keep you alive until you get help, whilst not being so powerful as to kill you? I could be completely wrong thought! But it's always been my fail safe...
If it's an option for this individual, smoking some pot might help against the nausea and retching. Best thing for opiate nausea as far as I'm concerned. I'd personally just try to give their stomach a rest - sometimes drinking more water will just induce more vomiting - the only thing that will really help is just time, until the drug in question wears off.
Sometimes too just laying back in a reclined position can help a good bit. If you're on the edge of having taken too much though it is very important that you have someone to watch over you to make sure you remain awake, and things don't go south.
Keep replacing electrolytes....energade, powerade, gatorade etc.
This will prevent dehydration.
And quicken recovery time.
When he feels up to it then he can eat solid foods.