Originally Answered: my dog ate m&ms (i didnt feed him it)?
Hm. A bag of m&ms isn't normally enough to make a 30 lb dog ill, but your dog is clearly sick. It may be a combination of the sugar, caffeine, and theobromine, but vomiting and excess thirst are two telltale signs of theobromine poisoning. How long has it been? If it's been less than two hours induce vomiting. Feed him a tablespoon of hydrogen peroxide, one at a time, until he vomits. Call your vet and ask for advice, a phone call is free.
If your dog is not looking better within 24 hours surrender him to somebody who can provide veterinary assistance. Theobromine poisoning can take up to a week to kill a dog and if this has happened and he's having an acute reaction then he may experience neurological dysfunction and/or organ failure. If your dog begins showing symptoms of lethargy, hyperactivity, vomits or poops blood, excessive urination, excessive drooling, shaking, seizures, muscle spasms, or anything else out of the ordinary he needs to get to a vet immediately.
Inability to provide veterinary care is inexcusable. Saying you cannot take him to a vet does not make home remedies suddenly appear out of thin air. If such remedies were readily available, practicle, and at all reliable then the vets would be out of business. Failure to provide veterinary care is a criminal offense and is punishable by fines and jail time. Please reconsider your ability to care for this dog if you cannot provide basic veterinary care in the form of a $40 checkup and $50 for blood work. Consider borrowing money or applying for care credit. Some vets still offer payment plans.