I know people say you can buy stuff but it can be hard to find or much more expensive. Heres a quick list I wrote for my Turkey holiday 2 weeks ago!
Lots of suncream we had 6 tubes
Plug adaptors, mosquito spray, wet wipes,
Charging sockets and leads
Calpol / Hayfever medicine / Nurofen
I always take my thermometer and nit comb ! (memories of discovering nits whilst abroad and no nitty grittys in site - ugh!)
Thats all literally one bag of toiletries.
Then I take small shower gel / shampoo / conditioner / body wash as Im allergic to most fragranced ones.
Holiday insurance, car parking at airport or cabs
Ipads etc with films already downloaded from Netflix
Swimming goggles and 3 swimming costumes each in case they dont dry at night. I always take a small bag of paracetomol, plasters etc as again if you are in a resort you can be no where near a pharmacy.
Also take a big beach bag - if you are in a resort it can be a walk down to the beach with towels, goggles etc. Doubles up as a shopping bag too.
We take inflatables for kids to use in the pools or beach and a pump as inflatables can cost £15 upwards abroad and kids love being in them.
Aftersun and cardigan or sweatshirt to wear on the plane or if you get back late at night. we got back at 5 am on Sunday when it poured with rain and the kids were cold.
Books / magazine / sticker books for the plane in case devices run out of charge due to delays. Snacks - for the way out I shove a banana, granola, chocolate etc into my rucksack as again someone is always hungry at the wrong time. some of the above will depend how old your kids are. If yours are younger I also used to take their formula as they didnt like other brands, and Ive even been known to pack a Bumbo! But I am good at squuezing everything into teeny places!
Hope this helps.