A large bed with posh mattress. A change of bed linen and a blanket in case it gets cold.
A decent shower.
More than one towel. For the money that's being spent, give us enough to dry ourselves.
A tumble dryer. Saves you having to deal with wet towels strewn across the bathroom because there's nowhere to dry them.
A washing machine with a quick wash function and some washing powder tablets.
Tea towels or kitchen roll. A spray cleaner for the kitchen and any spills.
A small bottle of washing up liquid.
More than 1 chipped mug and 2 glasses.
A kitchen knife that actually cuts, a fish slice, slotted spoon and a colander.
A potato peeler, can opener and bottle opener.
If the fridge has an icebox, finding ice already in there is brilliant. Or if you're really fancy, an American fridge with icemaker.
A mop, bucket and broom/dustpan and brush.
A decent non stick pan.
Bin bags.
Somewhere to hang clothes up. It's all very well having magnetic locks on your built in wardrobe to keep your stuff safe, but it would be nice to be able to take clothes out of bags and at least get some creases out by putting them in the bathroom whilst the shower is on.
Wifi.
Salt and pepper in the cupboard.
It would be marvellous if there was a small jar of instant coffee, a box of fresh teabags and a pint of milk in the fridge.
Do all those things and you'll a) have a clean and tidy property to go through as quickly as possible for turnaround and b) probably get a repeat booking.