Some vehicles have a full-size spare, some have a temporary spare and some have a repair kit instead. Open the owner's manual and look at the actual vehicle before assuming what is underneath the cargo floor. A used vehicle may also be missing equipment that originally came with it.
Find the spare's location and check how it is accessed. A release tool stored in a separate compartment is part of the system. If a wheel-lock key is required, know where it is and keep it available rather than leaving it in a drawer at home.
Check condition before the journey
Inspect the spare for obvious damage and have concerns assessed by a qualified tire professional. Check its pressure when cold using the vehicle manufacturer's instructions for that spare. The recommended pressure for a temporary spare may differ substantially from the road tires; do not simply copy the value from one to the other.
Tires age even when they are seldom used. An unused-looking tread does not establish that a spare is suitable for service. Follow the vehicle and tire manufacturers' guidance on inspection and replacement, and ask a professional when the age or condition is uncertain.
Check the associated equipment too. The jack, handle and wheel tools need to be correct for the vehicle and stored securely. Do not substitute an unfamiliar jack or assume that a lifting point is safe because it looks strong. The manual identifies the intended equipment and procedure.
Know the boundary between preparation and roadside work
Read any speed, distance and load restrictions for the spare before relying on it. A temporary wheel is not a reason to postpone proper repair indefinitely. Keep those limits available with the vehicle information so they are not another item to search for after a disruption.
A roadside location may make changing a wheel unsafe, even if the necessary equipment is present. Moving traffic, soft or sloping ground and poor visibility are reasons to seek assistance. Never get beneath a vehicle supported only by a jack. Preparation can include knowing how to contact help rather than planning to perform every repair yourself.
Finally, load the car for the trip and check whether the spare compartment remains reasonably accessible. If retrieving it requires unloading heavy luggage into a dangerous area, plan for professional help and keep essential communication items elsewhere. The goal is to remove surprises before travel, not to guarantee a particular repair can be made in every location.