I now have a 'holiday packing list' - with a section to add on for 'hot / water holidays' and a section for UK holidays (where you inevitably take more income maybe food etc) and a section for 'cold holidays' with coats, hats etc. I keep this in a folder and get it out the week before we go, so I don't have to write it every time.
This means I'm not scrabbling around the house at the last minute trying to work out things to pack. It stops a large part of the stress before. DH has been delegated electronics and cables because he drives me nuts with this because he wants certain ones - so it's now his problem to solve whilst I work out everything else. This has stopped so many arguments! I realised it was my weak point and it was better to delegate one task and do everything else rather than packing together too.
Eating out. I get very stressed about this and find that knowing the menu beforehand is a really good way to deal with things. So I now either look up restaurants on trip advisor before I go and look at comments, ratings and menus - and pick a few (so when one is closed unexpectedly / full, you have a plan b). Or we scout out a few when we get there, take photos of the menu and then go back on another day. This way you can help with the kids expectations and say 'we are either going here or here - it depends on which is available. If we go here we will have this, or if we go here we will do this'.
The pack of cards (game of your choice) - especially when your kids get a bit older. They are easy to carry. It means you all interact with each other and the kids are engaged and you have family time. Then (if you absolutely must) devices. But cards first. Having something to do in a restaurant whilst you wait is brilliant. If you have a kid who mucks about the chances are you aren't going to want to go to somewhere swanky where you are going to get stares for doing it.
Eat out at restaurants at lunchtime not dinnertime. It's cheaper, and the kids are better behaved. You have a nice time and you'll all be less hangry. By the time you get to the evening the kids are knackered but they won't be as hungry because they've had a big lunch. Thus doing an evening meal is easier for you and if they do play up it's at the accommodation so you can manage it better.
Also see the supermarket picnic option here as a back up to - bread rolls, packet of sliced cheese or meat, big packet of crisps, drinks as a cheap alternative to eating out. You can always find something that fits this as a rough plan. The kids get used to it, know what to expect and it's cheap. You also aren't fancying around as it's easy to do on the go. (I find foreign supermarkets are fun in their own right). This also means if you find yourself not near the place you planned to eat out, you have an easier alternative if need be that you can do on the fly.
Also simple things like making sure the kids have their clothes out for the next day, when they go to bed. So they know expectations and there's less faffing around when you want to get out the accommodation. Have a bag packed with as much as possible. That way you minimise the arguments in the morning getting out the door. The less you have to do before you leave in the morning, the better.
Honestly it doesn't sound like much or like it will make much of a difference but little things can help to relieve the stress points - these are just some ideas. The key - Identify your stress points on holiday. Start to think of ways to make these stress points easier by having routines from home that follow you and you have routines on holiday that you all know as 'what you do on holiday'. This means everything can be different but they can also feel more familiar and more 'safe'.
Don't try and do too much. This is the fatal thing. Yes maybe plan to do x,y and z but learn it's ok and wise to drop y if you need to. Trying to do too much tends to be a killer. The trap is you want to 'make the most' of the time and keep the kids busy. If you are having a good time, don't feel you have to leap to the next thing. Embrace it.
Simple tricks that work for YOU will make the whole holiday better for the kids, who then don't kick off as much so you enjoy the holiday better. It's a vicious cycle - work out what's causing the most aggro.
(Yes I've been there).