Trekking Poles
Besides helping you be more stable while hiking on treacherous terrain, like water crossings, steep up or down parts of the trail or loose ground, trekking poles (aff link) might also double as your tent poles. Some tents aren't freestanding to save weight and you have to use sticks or hiking poles to keep it up.
Or triple as a selfie stick.
As with all other outdoor gear, there is a wide price range and a few different materials to choose from. Aluminum or carbon fiber is standard for the main body. Cork or other soft material for the grips. Adjustable height and different tips based on the terrain you're in are also pretty standard.
If you're a member of Costco and you time it right, they have really good carbon fiber pair (2 sets) for a great price.
Your local recreational store will have options as well as Amazon.
Why should you use them?
• Stability
• Lesson impact on your knees
• Balance
• Weight distribution
Trekking poles might not be needed all the time, but a good piece of gear to add to your kit. You can just carry them at your side when the ground is nice and level.
If you're day hiking or thru-hiking, they might just keep you from taking a tumble, save your knees and help pitch your tent.