Much, to my mind, will depend on where in Europe you are going and how long you expect the drives to be. They may be as short as a quarter hour in some places like Poland with 12-20 drives in the day and very quick moves between each drive OR each drive may be half a day. Or you may be sat on a platform/box. ALL the above advice is good.
My kit list (part) used to read like this:-
Hat and Red Hatbands, Cammo Hi-vis vest,
Daysack- field dressing, spare ammo, pullthrough, saddle flask & s/steel beakers, dragrope, sanglier pullover, marker tape, camera, waterproof trousers, permis & insurance cert’., [I am not well upholstered so in the early days I used to take a very thin thermal (closed foam) cushion to sit or kneel on for long periods,
Shooting jacket, field dressings, pull through, scarf, gloves,
Trousers, socks and garters, knife, hankie, [ear defenders], loo paper in a re-sealable bag,
Thermals (1 set) and shooting shirts (2), tie, Cashmere v-neck [all the layering principles apply],
Rifle, ammo and muzzle cover, spare battery, rifle cover (legal req’ment in some countries),
(Tripod) Shooting stool, [more stable than a British monopod shooting stick and because it was taller I can stand instantly off it, [Edit - too bulky if you are flying there.]
Wellies and welly socks - or thermal boots if you are expecting really cold temperatures,
Thermos flask and sandwiches or sweeties depending on how you will lunch.
Go and enjoy and I shall confess to some envy. Weidmannsheil!
[Edit] I have just read your latest post whilst searching out my old list - I have been to Turkey several times but not for boar; the mountains are high and can be cold in the interior in winter. There are some huge boar there, usually stalked rather than driven. Locals hugely friendly. ]