I'm not sure why everyone is suggesting "no people food".
Some people food is actually good for them ( pumpkin, green beans, carrots) and a little lean beef, pork, or chicken can be a real treat.
Granted, fatty meats are bad ( pancreatitis as mentioned before ) and junk food is a definite no-no. I try to avoid large quantities of dairy ( i.e. cheese ) with mine as well.
One thing that you do not want to feed them is: ONION.
Onions can wreak all sorts of havoc with a dog's digestion and most vets consider onions toxic.
Eating grass is not necessarily a sign of stomach upset. I could count on both hands the number of times that my nine year old heeler showed any signs of indigestion when she went grazing. Many dogs, apparently, just like to eat the stuff or maybe they eat it to prevent indigestion.
Normally I feed my dogs DRY FOOD twice a day. It is important to know the weight of your dog and follow the feeding guide on the bag for portion control. If you have a dog that chokes on dry food, add water to it.
For constipated dogs, add green beans or pureed pumpkin to the food.
When I say I give mine people food, I mean 1/4" squares of cheese, an occasional piece of carrot and once in a while, if they're really well behaved, they get a dab of peanut butter on a saltine.
If you have the time ( and preferably a breadmaker ) , you can bake your own dog biscuits. Not as fancy as store bought, but at least you know what goes in them.
Dog biscuits:
3/4 cup hot water
1/3 cup vegetable oil ( or olive if you have the bucks for it)
1/2 cup powdererd milk
1/2 teaspoon salt
1 egg
1 tablespoon peanut butter
3 cups flour ( I use whole wheat )
Mix it up, knead until stiff, use something for a cookie cutter, and bake in the oven at 325 for 50 minutes. bacon bits, pretzel bits. or any other dry sort of ingredient can be added to the dough for flavor variation.
If the dog hasn't been wormed, get it done. Worms don't just live in the gut... they lay eggs there too.
Also, keep a bottle of hydrogen peroxide on hand. If you think that your dog has ingested poison, call the Animal Emergency hospital in your locale. If they say induce vomiting, start dosing the little critter ( I use a shot glass ). Do it outside, though.
And finally, do not allow your dog in the garage if you have any coolant on the floor and do not store bottles of coolant on the floor.