The short answer for a Devon Rex
Seven days is the floor for a Devon Rex, and two weeks is the safer target. A Devon Rex is a small, lightly built cat with a thin wavy coat and very little body reserve, so she feels a missed meal or an empty bowl sooner than a sturdier breed would. Emergencies also stretch: a road closure or a night in temporary housing can turn a planned two-day absence into most of a week, and the store you counted on may not be open when you reach it.
Working out the amounts for this particular cat
Base the Devon Rex's water store on what she actually drinks now, not on a generic chart. Watch her bowl for a few ordinary days, note how often you refill it and by how much, then multiply that daily amount across your storage window and add a generous margin. Stress, travel, and a warm room all push a Devon's thirst up, and her large ears and fine coat do little to hold heat or moisture in. For food, count her measured daily portion, including the treats she reliably gets, and store that exact food. A Devon stomach that is used to one recipe should not meet a brand-new one in the middle of a power cut.
How to store the Devon Rex supply so it stays usable
Keep the Devon Rex's food in its sealed bag or in an airtight bin, off the floor in the coolest dry cupboard you have, with cans stored where they will not freeze or bake. Bottled water keeps best away from sunlight and fuel smells, so a hallway closet beats a garage corner. Split the supply into two places if you can: a grab-and-go portion beside her carrier, and the larger portion where you would shelter at home. Write the portion size on the bin in marker, so anyone feeding her during the emergency gives her usual amount rather than guessing.
Rotating the store before it goes stale
A Devon Rex emergency store only works if it is fresh on the day you need it. Bring the oldest cans and the open rotation bag into her normal feeding first, then replace them with new stock, so nothing sits untouched until it is hard, rancid, or refused. Check the water bottles whenever you check the food and swap any that look cloudy or have lost their seal. Do the same sweep of her carrier, harness, and a spare blanket at the same time, because a Devon with her fine coat chills quickly in a draughty hall or a cold car.
If the emergency separates you from your Devon Rex
The risk that comes with any evacuation is a frightened Devon Rex bolting from a carrier door or a strange doorway. Keep her collar and identification current, photograph her distinctive wavy coat and large ears from both sides, and note any feature a stranger could use to confirm it is her. Those details matter far more for this unusual-looking breed than a general description would. When a separation does happen, KinsLe's Lost Pet Alert System sends her alert out to nearby members of the Circle of Love, so the people best placed to spot a scared Devon Rex are already looking.