Apparel, Jewelry, and Accessories
If you want to go the clothing/jewelry route, you have lots to choose from. ThinkGeek has a pretty dope messenger bag for sale, perfect for carrying some books or a tablet. It’s a little pricey but if someone is a big fan, it would be a great gift.
The official Halo Waypoint Store, has a ton of accessories to choose from, as well. There are hats, wallets, keychains, jewelry lanyards, and more. All of which are pretty fairly priced, at least in comparison to most official stores. Visit the store and just click through the accessory page to see if there’s anything that appeals to you.
Finally, you could always go the t-shirt/hoodie route. Once again, the Waypoint Store has plenty to choose from for officially licensed stuff, such as this zip-up for only $30.00 (as of this writing). Redbubble has a lot more variety and is also worth a look, as well.