how good is he at finger food? Will you be able to feed him from the buffet? If not, bring enough jar/ready meal food for the first day or so until you can nip out to a supermarket.
bring bottles or whatever he drinks his milk/water/juice etc out of. At 9months you don't need to sterilize but a little bottle of fairy liquid and a bottle brush wouldn't go astray. You can take a tin of formula in your luggage (i am assuming he is not breast fed, ignore if he is) or you can buy it there if you are using a widespread brand. We used Aptimil with DD and was able to buy it everywhere we went in Europe.
Sunscreen, hats, sunsuit (cuts down on having to apply sunscreen to wriggly baby), nappies. When i took DD to Turkey at 4 months i only brought enough nappies for the fist few days and then purchased them locally. I didn't do that this year as we were going back to Turkey and i hated the Turkish ones (plasticy horrid things that in the 40 degree heat must have been awful to wear) but DD is now 16 months so wearing a lot fewer nappies iyswim. Take swim nappies with you though. THey always seem to be hideously expensive if you buy them insitu.
Most of the all inclusive places have cots that you can borrow off them, sometimes for a fee. If your hotel does it, book it now as it is much easier than trying to get about the place with a travel cot. All you need to take bedding wise then is a blanket or sleeping bag and cot sheet.
You might want to consider a travel stroller depending on how much sleep you think your LO will be doing in it. Most of the pushchairs advertised as "travel" ones don't seem to recline. You should be able to take your normal one though and it wont count as part of your luggage allowance.
Beware going through security with your changing bag. I have traveled with DD fairly often and they always waved through the bum cream in the changing bag without question but this year they demanded i chuck it (very very annoyed!). Also any food you are taking on the plane make sure it is in a resealable container as they will more than likely demand you taste it to prove it is not explosive.
You can probably get by without a booster seat etc. Most hotels, especially those who cater to the family market, will have high chairs you can use. If you are worried though get one of those cloth high chairs. We had one for DD when she was a tiddler and it was great. It wont boost them up though, just keep them from wriggling off the chair.
i think that should about do it. HTH. Have fun.