Record the accessory itself
Photograph a remote, cable, case or adapter individually. Copy any visible identifier. If its relationship to a particular unit is uncertain, mark the relationship as unverified.
Keep the source of the claim
Distinguish an accessory listed in a manual from one a previous owner included. A matching color or connector shape is not proof of compatibility. Check the product documentation before connecting anything.
Use an inventory label
Store your accessory record under its own number and cross-reference the related device. This lets you move an item between storage boxes without losing the note that explains what it is. Keep adhesives away from delicate finishes and original labels.