When a claim is made, the provider usually wants to see that the car was maintained the way the contract and the manufacturer describe. That means the dates, the mileage, and the work performed have to tell the same story. Most owners keep the receipts. Fewer keep the mileage that goes with them.
Make the log a habit, not a project. Each time the car is serviced, write down the date, the odometer reading, the work done, the shop name, and the invoice number. Keep it in a notebook in the glove box or in a note on your phone. The point is to record the reading at the moment it was true, not rebuild it later from memory.
Match the log to the invoice. A careful shop writes the odometer reading on the repair order. Check that the number on the invoice matches what you wrote down. If the shop left the reading blank or wrote an estimate, ask them to correct it while you are still at the counter. A mismatch is easy to fix on the day and hard to explain months later.
Photograph the dashboard when it matters. Before a long trip, before a drop-off, and before you hand the keys to someone else, a quick photo of the odometer is cheap evidence. Keep the photos with the same dates you record in the log.
Read the contract's upkeep wording. Find the clause on maintenance records and note who must keep them, in what form, and for how long. Some agreements describe acceptable proof in general terms. Others ask for the shop's own paperwork. Plan to hold whichever kind the contract names, and do not assume a store receipt with no mileage on it will be enough.
Notice the gaps. A long stretch with no entries is not proof that nothing happened. It is simply a gap the provider may ask you to explain. If you drove the car heavily through a season with no service, write that down too, along with the reason. A plain, honest note is more useful than a log that looks too tidy to be real.
Keep the records as long as the contract matters. Store the log and receipts with the contract copy, and keep them after the car is sold if a claim could still reach back to an earlier visit. Digital copies are fine if you can open them years later. Printed receipts fade, so scan them.