Coat hooks
Oven gloves
Towel in the kitchen and somewhere to hang it
Dustpan + brush. I don't really clean while we're away, but if I drop stuff I don't want to be treading in it for a week
Enough dining chairs and comfy chairs for everyone
Somewhere to put a washbag or toothbrushes etc. in the bathroom other than the sink or the floor
Space for food we've bought, no we don't want to have 10 cupboards full of random china and nowhere to put the pasta
Sensibly chosen stuff, e.g. not plates that are too big for the dishwasher, and more than 4 forks etc. for 4 people, so I can use one while cooking and not have to wash it up to eat
No cushions on beds
Thick curtains
Extra blankets somewhere for people DH who feel the cold
More than one key
A welcome basket isn't essential, but it's nice
Much of this stuff you don't find out till you get there and are hunting round in the kitchen for a grater or a chopping board. But when I'm choosing between available cottages, a big plus is somewhere that looks cosy and has character. If I see a living room with white walls and no pictures, and the only furniture is a couple of brown sofas and a telly then it's a no from me.
And I don't care about king size beds, but I don't want anyone in our group having to sleep either on a sofabed or in the living room.
I also don't care about TV/Netflix as we never watch it on holiday.
A few people have mentioned salt, pepper, oil etc. I really like to have these in the house, but last time I took my own (plus a week's supply of dishwasher tablets, some foil etc) as I've got fed up of having to buy a bunch of stuff each time, just to use a tiny amount during the week. It's a particular nuisance if you are flying and don't want to lug extras back and forth.