Everyone's spare parts locker is different, based on your boat and equipment, but here is a general list of spares and products that might be found on a well-stocked vessel.

When assembling spares, you don't have to go it alone. Check with your engine's manufacturer and some of the major distributors. They sometimes sell spare parts kits that, while often containing expensive brand-name parts, are guaranteed to contain filters and belts that match your engine. It's a good place to start.

Remember that your engine is not the only piece of equipment that requires spares. If you have a generator or an outboard for the tender, they too need a kit.

Remember too that spares don't last forever, and storing them unused for years is not the best practice. A better strategy is to install your spare parts when you have regular service done, then buy new spares. This way, the parts on the engine and in the locker are new.