Many folks forget that Devils Tower National Monument is in the high plains of Wyoming at an altitude of over 3,700 feet. Winds in the area can be strong and it can snow as early as October and as late as May. When we there on a May day the morning temperature was down in the high 20's early in the morning.
Toiletries and Medical Supplies: Sunscreen to avoid the sun.
Photo Equipment: Zoom lens to get pictures of the tower and climbers ascending the tower.
Camping/Beach/Outdoor Gear: Camping is extremely reasonably priced. Prices posted were $ 12 a night for a campsite and only $ 6 for seniors with Golden Eagle passes.
If you want to see Devil's Tower, then you should expect to do some walking. The trail leads all the way around the monument, and it may take an hour or so to get around, depending on how fast you are and whether you stop or not. With this in mind, it is best to wear shoes that will be comfortable, and shoes that you don't mind wearing out or getting dirty.
Miscellaneous: You may want to bring some water bottles if you think you may get tired or dehydrated.
Be flexible. Weather can change over night. Summer, hot and dry, cool at night and the Winter is cold and windy. Take good walking shoes, as you will not want to stay in your vehicle.
Photo Equipment: Take the best camera you can with a lot of film for photographing, as this is one of the most scenic areas in the United States with a lot of wildlife.
Hiking shoes of course, a warm sweater or jacket for nighttime.
Photo Equipment: Polarizing filter for sure. A good zoom lens for the Prairie Dogs. Lots of memory.