Every product I talk about is available on Amazon US and hopefully Amazon UK plus all linked for you to purchase for yourself.
I want to start off with a dual pack Xbox One Play and Charge Battery Pack from KELUX. It’s selling for about $18 ($17.99) but the shipping may differ depending on where you live. You will be granted with excellent performance and a long life battery for gameplay. It even provide you with the ability to charge both controllers while having them in use. (Amazon US)
Even though the Xbox One has a HDMI output and pass through I still recommend buying the HDMI Switch Selector by Etekcity. It’s selling for about $7 ($6.99) but the pricing may differ depending on where you live. Play games in 720/1080 resolution as well as 3D via the HDMI output. (Amazon US)
My last gift idea would be to buy Microsoft Gift Cards that range from $5 all the way up to $100. The best part is that you can choose between an online game code or a physical card. This allows you to purchase games and entertainment for the Xbox One, Xbox 360, Microsoft Online Stores, and Windows Phone 8. This could include games, map packs, music, movies, TV Shows, and much more. (Amazon US)