Bless you for rescuing this kitty. It sounds as though it may have an upper respiratory infection. Usually, these aren't too serious and can be treated with antibiotics. If the kitty will eat and drink for you, then it is safe to wait until Monday morning to run him into the vet so they can check and give him some antibiotics to clear up his head. If he's feeling bad, he won't play much and will try to save his energy for getting well. Your most important job for the next day or so, is to keep him indoors, and provide plenty of fluids and if you can get some Gerber Baby Meat (turkey or chicken) to try to tempt him to eat. If cats can't smell their food, they can't eat, so it's important that the vet get him started on antibiotics to clear up the sneezing before it gets to where he can't breathe out of his nose. It is normal for cats to sleep a lot anyway, but you are providing him a safe place to be for now. If he starts acting extremely ill, you may need to take him to the emergency clinic, but for now, I think he'll be fine until Monday morning. Just watch him to make sure he is urinating when he goes to the litter box and isn't making a lot of trips without doing anything.

Please let me know how things go, and again, you are wonderful for saving this guy!