A bandana or similarly sized non-cotton cloth is an essential backpacking accessory. Multiple uses from wiping your forehead or nose to helping keep sun off the back of your neck. I like to hang mine on one of the loops on my pack’s shoulder straps for easy access while hiking.
When you return from any backpacking adventure, it’s always a useful exercise to lay out everything you carried in your pack and see if there is anything you didn’t use. Doesn’t necessarily mean you should leave it behind next time (like rain gear, or a small first aid kit), but may help you be more disciplined in your packing next time.
Empty out your entire pack and ensure everything gets throughly cleaned and dried before packing away in your basement, garage, or closet. Even a little moisture can cause equipment to smell and perform less effectively over time.