The toxicity of chocolate is judged by the amount of theobromine in it. Milk chocolate (like the kind in candy bars), contains 60 mg per ounce of theobromine. The toxic dose is one ounce of milk chocolate per pound of body weight. For example one pound of milk chocolate is poisonous to the nervous system of a 20-pound dog. If you figure it all out, it ends up being that it takes 2-3 chocolate bars to be toxic to a 10 pound dog.
Of course, it is always better to be safe than sorry, and the safest thing to do is to induce vomiting in your pup. Details on how to make that happen can be found here: http://www.petplace.com/dogs/how-to-induce-vomiting-emesis-in-dogs/page1.aspx
The best thing to do is give him some peroxide. Then adopt a watch and wait posture.. The symptoms of chocolate toxicity include trembling, nervousness, shaking, increased heart rate, panting, and, worse case scenario, seizures or death. Dogs that eat dark baker's chocolate squares are at most risk of seizuring or dying from chocolate. I would also keep an eye open for tense stomach, attempting to vomit or defecate with no success and abdominal swelling as this can be a sign of intestinal blockage from any leftover wrappers that he may have ingested.
I hope this helps!
If he ate the chocolate that long ago, then the odds of him throwing it up anymore are pretty slim.
I'd keep my eyes open when he defecates to see if there is any more foil coming out. As long as he's behaving normally (sleeping, eating, not acting painful, able to defecate without problems) then you're most likely in the clear. The foil may be small enough to just pass through without causing too much trouble, but I'd be diligent and keep my eyes open anyway, just to be sure.
More information can be found here: http://www.thepetcenter.com/sur/io.html , http://www.dog-health-and-supply.com/DogIntestinalObstruction.html .
Classic symptoms of an obstructed dog are: Mainly vomiting. Generally an obstructed dog will continue to vomit or dry heave even after they have stopped eating. Usually, they also do not produce much feces. Sometimes, they will experience pain in the abdomen. Any dog that vomits more than three times in one day, stops eating or defecating for more than two days, has a painful abdomen, or has a marked decrease in energy or activity should be seen by a vet as soon as possible.