Comfy beds are the top for me and decent pillows and duvet. I'm miserable if I don't get proper sleep. Proper blinds on any velux or otherwise high up windows, and decent thickness of curtains- I don't have young children any more but I've had to mock up curtains out of blankets in the past because of too much early morning sunshine waking up the kids at 5am.
Twin beds that don't have a footboard on if teenagers are coming. DS1 is nearly 6ft 3. DH's and mine has to be a king size, that is a standard bed size these days in holiday homes and hotels as far as I'm concerned. I would instantly dismiss an old fashioned double.
Proper size bath towels. Stayed in an independent hotel once in York which was so disappointing. Teeny double bed. And handkerchief size bath towels. Barely covered my arse, and I'm quite skinny but they weren't even long either so I just couldn't wrap them round me properly. They were more like large hand towels. Useless.
Decent shower, don't mind if it's a shower over a bath or a shower cubicle. Doesnt' have to be a power shower either. I just want a steady temp and stream (not a trickle). Bathrooms need either a window or proper extractor for ventilation.
A few tea towels, not just one.
Stayed in a very well equipped house in Dorset last year. We didn't have to buy anything for the kitchen apart from our food (and even then they'd provided a lovely Dorset apple cake, milk, tea bags, multiple sachets of sugar and coffee enough for the week and other goodies). They had full sets of tin foil, cling film, paper towels, handwash and antibac, dishwasher tabs, washing up liquid, surface cleaner etc. Fly spray, candles, matches, torch, plenty of bin bags and recycling bags, washing powder. All the cooking implements you could want. Was the best ever place we've stayed in terms of equipment and we've stayed in some excellent ones. No doubt you pay for that as part of your rental but I'd rather pay extra than have to ferry stuff there in the car, or buy it down there.