Definately bring your hiking shoes for walking around the desert trails. When we went it was winter (and cloudy) but in the summer I would suggest lightweight clothing as it gets very very hot
Toiletries and Medical Supplies: Sunscreen, there is hardly any shade at all.
Photo Equipment: if you want to capture any of the elusive wildlife, you might wast to bring a long lens. For Cacti details a macro is a great thing to have.
Miscellaneous: It is always a good idea to bring along water when you are hiking. Especially in the desert! The only place in the park to get water is at the visitor center.
Do NOT follow me! Don't wear sandals when you are going to hike along the park trails.
To reduce the chance of being bitten by venomous snakes, scorpions or Gila monsters better wear boots and loose fitting pants while hiking.
I didn't meet any venomous creatures there :-)
Luggage and bags:
No bags in hot summer except one for your camera, good (safe) pockets (or comfortable belt) instead. Small city rucksack for warm winter.
Clothing/Shoes/Weather Gear: Light clothes (shorts, T-shirts, better too large :-) made of natural materials (cotton) for warm/hot days all year round.
Sweater/pullover and/or jacket for cold evenings/nights (from November till April).
Shoes? Oh, yes - you should have them :-). Sandals for walking and/or better good walking shoes for trails around (dangerous reptiles and insects possible).
Add sun glasses.
Check the 10-day forecast for Tucson:
National Weather Service
Toiletries and Medical Supplies: Good sun protection cosmetics with high UV filter - use them BEFORE or just after you leave your car.
Photo Equipment: Be prepared for large contrasts between sun and shadow - sun filters recommended. Add hmm... how do you call it in English - something fixed to your camera objective to protect it against sun - not comfortable to carry but necessary, I suppose.
Miscellaneous: Tourist frige with ice cubes and cold beverages inside :-).