FlorenceUK: Last year my DS then 10m had 4 general aneasthetics in 5 weeks: younger, so probably easier, but you may find the following useful:
What time is the operation? they usually put little ones in the list early, in which case the starvation isn't as hard to handle. We found distraction the easiest approach. Have you checked the latest he can have water/clear liquid to drink? Starvation times aren't as long for small children as they are for adults: phone and ask specifically about children his age.
Have you had a pre-assessment appt with the aneasthetist? They should come round and talk to you before the actual op. Ask if they can knock him out with gas before inserting a canula for the IV aneasthetic, as it is far preferable. The aneasthetic is, emtionally, the hardest part. If they use gas, which is administered through a face mask, the more he struggles, the faster he will breathe it in, and tho' it will feel like an age, I promise you that he will be unconscious in less than 10 seconds. I held him on my lap and the aneasthetist put the mask on from behind. Seeing your baby asleep on the big trolley is also v emotional. Have your dp or best friend or ANYONE waiting for you!
Make absolutely sure that you know where they will come and find you once the op is over. Generally they will let you into recovery before he is fully awake. We found that instant cuddles cleared up any post op tears immediately: he drank, ate and then slept soundly. Have easy to eat, favourite nutritious food availble for him.
Check with the aneasthetist about any post-op pain relief. Sometimes they administer something powerful before they come round if appropriate/necessary. Our DS had extensive surgery to re-arrange all the bones and soft tissue in his ankle and foot, and we had no problems with post op pain at all. You can give paracetamol and ibroprufen alternatively, so that you can 'leapfrog' them so it never wears off.
Remember that you will not be able to use your mobile in the hospital. If you are likely to have anxious relatives, (esp grandparents, IME!) calling incessantly for news, make an arrangement for leaving a message with them: you will wnat to spend time with your DS, not running round using the phone in the hall!
Don't know how long the op is, but have someone to be with. Our DS's surgery was 5 hours, 1st time, but even the 30 min ones were hard.
Take food and drink, and magazines for yourself. You won't want to run to hospital canteen.
Day surgery may happen in a special Day unit: if you are on the children's ward, prepare yourself: they can be emotional places, with children who are much, much sicker than yours.
The most important thing to remember is: the whole thing is MUCH worse for parents than the kids. Honestly! Our DS shrieked with delight and recognition each time we went back, excited by the clanky cots, wires from walls, attention, etc etc!
Good Luck, and let us know how you get on.