Starting hiking can be as simple as gym shoes and a water bottle if you're sticking to easy trails. As you're learning the area and deciding what types of hikes you enjoy, you can add to your gear. What you bring will be different for each category of hike: short day hikes, full day hikes, scrambling, or backpacking. I started with cheap, used, or borrowed gear, then upgraded over time. Here's a general list to get you started.
"The one thing that's more important than any gear you carry is good planning before you start the trip."
Pack A waistpack is lightweight and keeps your back free if you're scrambling. But a camel backpack carries more gear, and lets you drink hands-free, which is nice when you don't want to keep stopping for a drink. It's a chore to clean, so you might save it for longer trips or fast pace. Shoes Should have treads on the bottom to provide good traction on rocky terrain. Many people like the ankle support from boots, but some wear gym shoes (as long as the bottoms aren't flat or smooth.) Long hikes definitely need good foot comfort and protection, or you'll get blisters and endanger yourself.
Clothing Wear layers so you can adjust your clothing based on the changing weather. A long-sleeve polyester shirt will protect you from UV, and act as a wind breaker if you're chilly -- or cool you off if you're hot (wet it, and the evaporation will chill you.) In cooler months, wear a wicking layer on your skin, then an insulation layer for warmth, and a waterproof wind breaker on top. For pants, wear something that doesn't rip easily, preferably a synthetic fabric since denim and cotton get cold and irritate skin if they get wet. Think about the possible changes in weather, and what might happen if you get delayed hours or forced to stay out overnight, or several nights. UV protection like a wide-brimmed hat, sunglasses, sunblock, and UV chapstick are essential, even on cloudy days. Gloves keep your hands warm, and help avoid sharp rocks when scrambling.
Food & Drink Energy snacks with electrolytes are important for the desert. Sports drinks are full of junk sugar and contain only a few percent of what you need. Good things to target naturally are sodium (easy), chloride (salted snacks, olives, tomatoes, celery), potassium (banana, avocado, fresh or dried oranges, melons, raisins, prunes), calcium (milk, cheese, yogurt), and magnesium (leafy greens, whole grains, nuts, peanut butter.) Always bring more water than you think you'll need. In fact, drink tons of water hours before the hike, because your body takes time to hydrate, and then you won't need to carry as much. If you "feel thirsty", you're already dehydrated!
Poles Trekking poles come in handy if your trail crosses water or has loose footing on slopes. One is enough, but two provide better support.
Survival Kit Base your kit on the terrain, possible weather, and the time or distance to get help. One example pack has a built-in whistle, a microlight clipped to your pack, a compass with signal mirror built in, and wear a bright piece of clothing. Then add a map, LED headlamp, pocket knife, foil blanket, fire-starter, rain poncho, toilet paper, small trash bag, paracord rope, construction pencil, and paper with your name, contact info and medical alerts.
First Aid Kit This kit also varies on your terrain, possible weather, size of group, and the time or distance to get help. Here's what I carry: Field guide to first aid, antiseptic wipes, antibiotic gel, large bandaid, rolled gauze, ace bandage, chemical ice pack, duct tape, moleskin, tweezers, non-latex gloves, tampon, hand sanitizer, safety pin, splint, and bug spray. Include medications for personal use only, such as ibuprophen, imodium, antacid, benadryl, chewable aspirin, epi-pen, albuterol, etc. Adjust for the trip, like more for scrapes if you're hiking across desert, versus more for sprains if you're scrambling.
It may sound like a lot, but you learn over time how to cut things down into travel sizes so you can pack tight and it all fits in little plastic box. Hiking with a group helps because people can pool their resources if trouble arises.
Read more about the Ten Essentials for Hiking to be ready for emergencies. I also recommend the Wilderness First Aid classes available through the Red Cross or at REI.
Overnight Trips If you're backpacking, you'll need to add a bunch of stuff, but each trip I host usually comes with a suggested gear list. For example, here's our list for six days in Havasupai, Grand Canyon:
Backpack and small daysack, tent, sleep pad, sleeping bag, inflatable pillow, water filter, ready-foods or dehydrated meals, water shoes you can hike in, three outfits and six underwear, bathroom/hygiene products, backpacker stove and fuel, bowl and utensil, hat, sunglasses, sunblock, headlamp, bathing suit, first aid kit, dry-sack, trekking poles, and a camera.