My Dog still has testicles sak after being neutered.Is this normal. 911 question, is this a common thing. What should we do about it?

He should still have the actual sac, however if it is very swollen I would call the vet in the morning. Some swelling will be normal, but excess swelling and tight looking may need a quick look by the vet that did the surgery.
The sac should look like a floppy piece of skin.
If he is a very young dog it will most likely not be visible after he completely heals.
If he was older when neutered he may always look like he is carrying around a little "coin purse"
Was he neutered recently?

I concur with exactly what LadySam says. Our dog was neutered approximately 2-3 weeks ago and in the very beginning the sac was much smaller, but perhaps some swelling. Now it is as LadySam describes, it looks like a little coin purse. I, like you thought nothing would be there. But that is not the case. Actually, in the beginning they did not put the proper size collar on him and he was able to lick it. I took him back in and they gave him a larger collar and antibiotic because it was heading into infection because he licked it. So it was a little swollen and red in the beginning, but now everything is fine. :-)