To make up formula abroad you need to use boiled bottled water with a low sodium content see here, but if your weight limit allows I'd just take cartons. Your hotel can probably supply a steriliser or just take washing up liquid and Milton.
I wouldn't bother with jars tbh other than for the journey, most 11 month olds will eat pretty much anything. My 10 month old would be quite happy, i might take a few Ella's pouches (lighter than jars and won't break) but don't forget to check the baby likes them before you go! (Bitter experience!). Another advantage of pouches is that by 11m baby will be able to suck the food out instead of you needing to spoon feed, much less messy. DD has this down to a fine art at 10m!
For the plane, you can take baby food/formula through but you have to taste it, so useless really. Most airports have a little boots or other pharmacy and I just phone to check the have the formula I want in stock and buy there, after going through security, so I can take as much as I want. Same with pouches for the plane.
Other useful stuff:
Buggy sun cover, parasol won't cut it.
Good sun cream this one is great for in the bag and v easy to apply. Comes in a bottle too.
Sling for at the airport - you can usually take your buggy to the gate but often won't get it back until baggage reclaim.
Take calpol and brufen sachets on the plane, just in case their ears hurt. And don't forget to give a drink on take off and landing, really helps their ears pop.
Swim nappies can be left to dry out and be reused if you run out.
Uv protective swim suit/play suit is invaluable. I'd take a few. Most of the supermarkets sell them quite cheaply nearing summer. With sun hats for the pool too. We used baby sunglasses in the pool but that was Australia and Egypt so bit more sun.
Travel change mat is v useful on the plane where there's no room to put creams/nappies etc.
Travel blackout blind if you have a baby that needs the dark to sleep.
Travel cot mattress - otherwise it's like a board, but I'm a bit precious about this as I've had 2 non-sleeping dc! I also take a sheet but dc have eczema and v sensitive skins.
Torch for night time wakings.
Oh and check your transfer time as you may want to take a car seat. It's usually cheaper to buy a cheap one here (kiddicare own make for example) and take it over (free on plane usually) than it is to hire one, plus the hired ones are often dirty or broken.
Make sure you have decent insurance, sorted early. We had a luxury trip to dubai planned when dc1 was 18m. He vomited (a lot) on the first plane and we had to cancel and come home. He had norovirus. But it could be chicken pox or a hundred other things.
Have a great time. It's a lot easier than you think it'll be!