The right policy is invisible until the moment you need it — which is exactly when a cheap one falls apart.
Skip the airline add-on and the one your credit card claims to include; both are built for the mildest inconvenience, not a cancelled trek or a hospital stay abroad. Read the policy's actual limits for medical evacuation — anything under $100,000 is not enough if you are hiking, diving or simply flying somewhere with expensive private hospitals.
Match the policy to the trip, not the destination on the brochure. A ski week needs winter-sports cover, a long-haul career break needs a policy that renews without you flying home, and a family trip needs a per-person excess you can actually afford four times over.
Buy it within a day or two of paying your first deposit — most 'cancel for any reason' clauses only activate within a short window of booking. Keep the policy number, the 24-hour emergency line and your policy PDF saved offline, because the one time you need it will be the one time you have no signal.