Cold does not usually kill an outdoor cat. Wet does.
Shelter: straw, never blankets
A cheap plastic storage tote, a cat-sized hole cut in one side a few inches off the floor, the lid taped down, raised on bricks or a pallet, and packed with straw.
Not hay, and not blankets or towels. Fabric absorbs moisture, holds it against the cat and then freezes — a blanketed shelter is often colder than no shelter. Straw is hollow, wicks water away and traps warm air.
Small is better than roomy: a shelter the cat heats with its own body works; a large one never warms up. Two exits are safer than one if there are dogs or foxes around.
Water matters more than food
Cats can find something to eat far more easily than they can find water that is not frozen. Use deep, dark-coloured plastic bowls rather than shallow metal ones, place them in sun where you can, and refill twice a day in a hard freeze.
Feed more, and feed on time
Staying warm burns calories. Increase portions in cold weather and keep to a fixed time so cats are not waiting in the open. Wet food freezes quickly — in deep cold, dry food left in a sheltered spot is the more practical choice.
Bang on the bonnet
A warm engine bay is the most attractive place on a cold street. Thump the bonnet or sound the horn before starting the car. It takes five seconds and it is the single most preventable winter injury there is.
Clear a path, and mind the salt
Shovel a route to the shelter so cats are not swimming through drifts. Rock salt and chemical de-icers irritate paws and are toxic if licked off — use a pet-safe de-icer near anywhere cats walk.
When to intervene properly
A cat that is thin, wet through, limping, or sitting hunched and unresponsive in the open needs help now, not a shelter box. Contact a local rescue or TNR group. If it is eartipped it belongs to a managed colony and someone is already looking after it — tell them rather than removing the cat.