Luggage and bags:
Aside from your usual luggage, a backpack that allows both hands to be free for scrambling: essential if planning to explore the area canyons/parks.
Clothing/Shoes/Weather Gear: What to bring depends on what type of activities you're planning to do (slickrock biking, rafting, rock climbing, etc.) but the majority of travelers are likely coming to visit Arches and Canyonlands so my list is specific to day hikers, and to the warmer months. Anything fancier than cargo shorts and t-shirts is WAY too elegant for Moab. Yes, you can go to dinner in them.
Fleece vest or pullover
T-shirts both long and short-sleeved: heavy, 100% cotton is the enemy in wet weather so quick-drying blends are best
Socks: a synthetic mix is best to avoid blisters
Hiking shoes or boots with a good tread: the stickier the sole, the better. No open-toe sandals
Water shoes in a plastic bag
Toiletries and Medical Supplies: First-aid/emergency kit for day hikers:
Pain-relievers (Advil, etc.)
Ace bandage for splinting
Whistle or small reflector (can use an old CD)
Small scissors and pocket knife
Spare pair of prescription eyeglasses, if you wear them
Any medications you must take on a daily basis (insulin, etc)
Medication for anaphylactic reaction if allergic to bee stings
Photo Equipment: Whatever you use. Do bring an extra charged battery, and a polarizing lens and small tripod/unipod is nice if you have one. As exploring the parks in depth involves scrambling, your equipment must fit in your pack or otherwise allow both hands to be free. Dust can be a problem so lens cleaner is a good idea.
Miscellaneous: 2 water bottles: this is ESSENTIAL
Snacks: nutrition bars, gorp, etc.
Small bag for hauling out trash - please leave nothing but footprints behind!
A note about walking poles: unless you're intending on doing nothing but flat hikes (a near impossibility in this area) I don't advise bringing them. Again, there are many places where you need both hands to be free.
Toiletries and Medical Supplies:
Traveling westbound on I-70, I always stop in Grand Junction, CO on my way to Moab. Grand Junction offers a wide array of goods and services including drug stores, liquor stores, mass-merchandisers, supermarkets, restaurants and lodging. The best place in town to find anything you may need is in and around the Mesa Mall, which is located at the intersection of US Hwy 6 and US Hwy 50. Grand Junction is an excellent place to stop on your way to or from Moab.
Miscellaneous: Buy beer before you get to Utah!
If you plan to buy beer/liquor/wine etc. make sure you buy it in Grand Junction or some other town outside of Utah. The beer sold in convenience stores and supermarkets in Utah is watered-down 3.2 beer. To purchase real beer, liquor, and wine you must go to a UT State Store. State Stores are open no later than 9PM, they are closed on Sundays and various holidays, and their prices are ridiculously high. The only caveat is that the state of Utah likes to protect its liquor monopoly. According to state law, it is illegal to transport alcohol into the state of Utah; however the risk of getting caught doing so is relatively low.
Moab has some amazing hiking and good shoes are a must. A great hike is Negro Bill Canyon to Morninig Glory Bridge but your feet will get wet. My wife and I wear Keen Newport H2s but my friends ended up buying Tevas so they wouldn't have wet hiking shoes the rest of the trip.
In other areas the slickrock requires good traction, sneakers don't work real well. We did the Fiery Furnace hike in Arches NP and one of the fellows slipped and slid his way through in sneakers.
Hiking boots, sun hat, sun block. A hiking stick can be of good use.
Photo Equipment: Your favorite easy to carry camera and lots of film. If you are using a zoom or telephoto lens a hiking stick with unipod capabilities, or a lightweight tripod will help you to stabilize your camera.
Luggage and bags:
Waterproof bags! You never know when your canoe will tip. We had 5 canoes and 2 of them spilled their contents.
Clothing/Shoes/Weather Gear: Bring an extra hat. We saw a lot of people with shirts tied around their heads because their hats ended up downriver (including one person in our party). Watershoes are a necessity.
Toiletries and Medical Supplies: Lots and lots of sunscreen. Bug repellant.
Photo Equipment: You will not find any electricity so make sure you have plenty of battery power. Keep your camera gear in a watertight contain when not using.
Miscellaneous: Bring lots of water containers (preferably full...). You cannot count on finding potable water along the way. The sources recommended to us were dry when we were there. Bring something to purify the water (in case you do manage to find some along the way). The river water is too silty to treat.
If you are off to the nearby National Parks like everyone else, be aware that you won't find much shade, so dress appropriately. A hat is very helpful.
Toiletries and Medical Supplies: Plenty of water is a must. Don't forget the sunscreen.
Photo Equipment: It's extremely bright. Slow speed film is called for if you are using a 35mm camera.
Miscellaneous: Buy the book "Guide to Moab, UT Backroads & 4-Wheel Drive Trails" by Charles A. Wells. The $27 spent on this book salvaged my trip. It is incredibly informative and detailed. All trails are mapped out and logged by obstacles and interesting points. All you have to do is set your odometer at the start of each trail and you won't be disappointed!
Solid comfortable shoes and light colored and weight clothes.
Toiletries and Medical Supplies: Sun screen. Remember it gets really hot when you are surounded by sand and rock in the summer.
Photo Equipment: Don't lose your camera like the guy I met at Delicate Arch. He had to hike to the arch two times in one afternoon with 100 degree heat!
Miscellaneous: Again, water and some food will really help in the summer months.
Photo Equipment: What every you do, don't forget to bring your camera!!
Miscellaneous: You will find different rock formations all around.
Camping/Beach/Outdoor Gear: I got a flat after the first mile, on the first trail. Make sure to ALWAYS have extra tubes as you don't want to have to walk several miles in the desert with your biking shoes!!!