I'm back 
Is he staying in overnight? Either way, plenty of light loose t-shirts for both of you - gets sweaty in there, and he may be sick after coming round from anaesthesia. dd wasn't, but some kids are.
Snacks for you, and drinks, and possibly drinks/snacks for him (they like to give crisps, toast, rough foods that promote healing and amazingly - although in lots of pain - dd took crisps but refused foods you might imagine were easier). If he's in bed for a while, you may not want to leave him in order to go foraging for refreshments.
Ice lollies helped dd stay hydrated both in hospital (I sent dh out to get them!) and back at home, when she wouldn't drink.
If your ds is one of the unlucky ones that is in lots of pain and won't swallow (dd was - but most kids find it much easier, some no worse than an ordinary sore throat) don't forget you can get painkillers from the GP or hospital in suppostory form. Just stay on top of pain relief.
Don't worry if your ds seems confused or upset whilst waking up from anaesthetic - its a reaction to the meds, as much as anything else, and he won't remember it. You will, of course 
DVDs, or books, or small toys or all the above for distraction before and after op. Before is almost harder, in a way, because they can't eat or drink and want to do both!
It can be very normal for kids to run a slight temp for a day after the op - if it goes away, then comes back after a couple of days, see a doctor: it could be an infection and will need treating straight away. But on the day, normal. (They forget to tell you sometimes, freaked me out)
Um....thats it for now, but if you search for old threads you will see heaps more! Also, for your own sanity, do post here after op if you are worried/have questions about the healing process....its not always a straight line, they can have a downward dip after a few days when the scabs (ick) fall off, they can have suddenly disgusting breath, etc etc. Someone here will know!
Most of all, good luck, and know that whatever the problem that is taking your ds into his op - having the problem go away makes it more than worthwhile!