Function is more important than style in this case. Select a bag that has a few different pockets and is lightweight. Keep your bag as light as possible. You will put all of your supplies in your bag for easy access. Grab a first aid kit so you have supplies for any injury. Make sure it includes bandages, gauze, antibacterial ointment, cotton swabs, tissues, alcohol wipes, thermometer, and hand sanitizer.   Bring common medications like ibuprofen or acetaminophen. SAM splints are lightweight and are useful to carry in case of injury. If you need an EPI pen, be sure to carry it. Bring an inhaler if you have asthma. You cannot have too much water when desert hiking. Dehydration is a serious possibility, so drink lots and drink often. The absolute minimum you should carry is one gallon per person.  When you are halfway through your gallon, it is time to turn around. Make sure you have extra water in your car to rehydrate after your hike. Desert temperatures can drop drastically as soon as the sun goes down, even below 50 degrees. Bring a jacket if you will be hiking past sunset. If you plan on being out past twilight, bring a thicker jacket and warmer clothes. Eat before, during, and after your hike. Your body will burn through resources quickly in the desert, so make sure you keep refueling. Eat about twice as much as you would on a normal day. Eat things like nuts, trail mix, or beef jerky to keep energized. It is also helpful to eat a large breakfast before your hike. Maps are a necessary tool to help you orient yourself in the desert. Compasses or GPS devices can help you orient yourself as well. You never know when you will need to scrape off a cactus spine, so bring a knife or multitool like a swiss army knife to be prepared. It is helpful to also have a headlamp or flashlight in case you are out after dark If you are injured or encounter a threatening animal, you want to blow a whistle so other hikers or rangers can help you. Clip this to your daypack for easy access. Blow the whistle loud and clearly if you find yourself needing assistance. Be mindful not to toss any litter into the desert on your hike. Bring a plastic shopping bag or a small garbage bag to dispose of any trash. You will want extra water, snacks, and maybe an extra pair of clothes. After your hike, it is important to refuel with water and food since your energy will be depleted from the desert conditions. Drink some water before you leave, and change into fresh clothes if you are very sweaty. Desert heat is no joke, so be over-prepared rather than under-prepared.

Summary:
Grab a lightweight backpack or fanny pack to store your gear. Include a first aid kit just in case. Pack at least one gallon of water per person, per day. Bring an extra jacket if you hike at night. Bring energy-boosting, high-protein food. Bring things to help you navigate, like a map, compass, and GPS. Include a knife, multitool, and flashlight for extra preparation. Pack a whistle in case of an emergency. Throw in a trash bag to remove any litter. Put extra supplies in your car for after your hike.