Jello, toast, chicken broth soaked saltines, plain scrambled eggs, string cheese, banana slices, pear slices (these are especially good), etc..
Also peppermint is very settling for stomachs, so let him suck on a candy cane. I know a lot of moms would think "Candy, right after he's been sick?" but believe me, it works really well to help their tummies feel a little better and don't worry about the sugar, it'll give him a little shock of energy until you can get some real food in his tummy. Candy canes are not only good for the tummy, they're good for putting a sick toddler in a better mood and they're good for the soul. I don't give my kids the whole thing, I just peel the plastic off of about half of the straight portion of the cane and once they're done with that, the rest gets put away. The crook part makes a good handle for the little ones.