I eat out quite a lot with my twins, who are now nearly 4 years. I am generally on my own with them, so the ratio is one adult to two tinies!
I basically stick to what I want to happen, and always have done. I don't take technology, and rarely take toys/books as the table just gets too chaotic and they won't eat if there's toys to play with.
I still put my two in high chairs if I'm on my own (at nearly 4 years). That way there is no getting down and running around without me lifting them out. I order quickly - if it's a menu I know then I order with the person who shows us to the table if I can. At least order your drinks with that person, and ask for breadsticks too.
Once the order is placed, I take then both to the loo. With hand washing, that kills 5 mins, and by the time you get back to the table, the drinks and breadsticks are there to provide a bit of entertainment.
When the 'where's my dinner' questions start, I talk about the restaurant. Point out the kitchen (open ones are great if you can see in to them), the waiter who writes it all down, the bar man who makes the drinks, the different things other people are having delivered, different sized glasses/plates blah blah blah. Keeps them entertained but also keeps them interested in the restaurant/food rather than thinking about being/doing somewhere else.
When the food comes I get a few mins peace while they satisfy initial hunger. I eat fairly quickly, but if they're far ahead then I'll order their pudding to eat while I finish my main. I may or may not get pudding depending on how things are going.
During this time there are normally at least one, maybe two toilet trips. I hope they'll reduce, as some of the trips are more about boredom than needing the loo (and it is very irritating taking two kids to the toilet while your dinner goes cold, when neither actually manages to go!).
Although this sounds very busy, I enjoy taking them out. I have to say that Bella Italia get a lot of custom from us because I can use tesco vouchers; it would be difficult to reconcile an expensive bill with such a dinner!
In your shoes, I would make the change in one go - next time you go out, don't take the iPad etc, maybe just a small book and some paper/crayons. Use the high chair (explain that it's about being high enough if he is resistant. Completely matter of fact - "you won't be able to reach the table without the high chair, so in you go") and challenge unacceptable behaviour each and every time ("Ben, this is a grown up place, and we need to be quiet/still/no throw things. If we can't do that, we'll have to leave". Take him out if he can't do it, have the same discussion outside and then go back in and try again).
It will soon sink in and you'll be that serene family you envy right now :) I reckon two, maybe three dinners where you have to put in a fair about of leg work and you'll have it cracked :)
Good luck!