Well as you see from my posts we did 18 national parks and monuments last summer, 4 over spring break and planning a trip for summer to Washington's Mt Rainer, Olympic, North Cascades then Oregon Crater Lake and over to Montana for Glacier. I am sure we will find some monuments or others....
Your desert kit has been great for my Arizona and New Mexico photos as well as Texas.
A historical one for things like Mt Rushmore, DC monuments, St Louis Arch etc
Of course the regions someone mentioned. Hiking elements, camping, caves (we have been to 4 so far), cliff dwellings (Mesa Verde, bandelier, Pecos etc
Yellowstone is a huge one with lots of features.
Waterfalls, trees, bison, elk, moose, lizards, wild horses (animal life), Mountains, petroglyphs, sunsets in the park, Great Sand dunes (brownish sand), White Sands National Park (I need a kit for this one...still looking)
Arches, Canyonlands, Bryce have the red rocks
Black Canyon of the Gunnison has black rocks...lots of rocks!
Hot springs (Hot springs national park)
I can ramble on...
I have lots of photos too...We have been to over 30 of the National Parks and countless monuments, national seashores, historic parks etc