The first thing thats important when having an iPhone is a case.
A nice, cheap and durable case is the Spigen Tough Armor case.
A Glass Screen Protector
A glass screen protector is great because it is essentially a second chance in terms of if you crack your screen. These screen protectors are typically glass and are very easy to remove and put on. For $8 it is a great purchase BECAUSE replacing the screen on a iPhone is about $100.
Blue tooth speakers are a great addition because they are easy to carry around and place where ever desired. They also greatly enhance the volume and the quality of the sound of the song that your phone is putting out.
Below are a couple of great bluetooth options.