Mobile phone accessories that are essential for the operation of your phones used to come with the boxes that are offered by the phone manufacturer.
Usually it consists of battery, charger, headphone, USB cable and CD.
But for each brand and model of the handset there are plenty of accessories are available for a price. It can be from the original manufacturer or from a third party.
When you are buying a third party product you must take necessary action to see whether it will match with your product. If you are in suspicion don't buy it as the accessory can damage your gadget permanently.
Also if you are buying any accessories that are coming with strong magnetic power for your Smartphone, think twice before buying it as the product may affect the LCD screen of your Smartphone. Like wise the covers and skins that are coming with the magnets can affect your LCD screen.
Also buying heavy sound capable headphones can damage your ear's hearing power.