Iron bars, cement, thin mattresses, old sheets, plain blankets, toilet, sink, stuff written/carved into the walls, painted cement floor, prison overalls, prison shoes, prison clothing and incidentals, a few toiletries (toothpaste, comb, soap, dental floss), light with a cage over it, reading table, books or magazines, photos taped to the wall of girl friends, wives, children or friends, contraband hidden out of sight (cigarettes, drugs, bladed weapons, money, syringes, electronics, lighters, food, cutting tools, etc), inmates (pacing, reading, sleeping, staring at the wall, doing sit ups and push ups, writing letters)
footsteps echoing down the walkways, coughing, talking, muttering, swearing, yelling, whispering, shoes squeaking, pages turning, water turning on and off, toilets flushing, humming, grunting/panting while exercising, mattresses squeaking, guards speaking/yelling, buzzers, iron door shuddering open, voices over loudspeakers, sirens, riots/fights
Sweat, metal, mildew, cleaning products, soap, air conditioning, food from the mess hall, dust, dirt
water, contraband items, approved items purchased through prison confectionery (cookies, chips, instant coffee, chocolate, etc)
Cold metal bars, cracked and dirty porcelain sinks, walls of pitted concrete, laying back on a mattress with no back support, springs digging into your back or no springs at all, lumpy pillows, scratchy blankets, piled sheets rubbing at your skin, running a finger over the face of loved ones in photos, flipping through magazines, a pen held tightly in fingers as you write a letter, sketching or studying for educational improvement, probing a bruise with your fingers after a scuffle with guards or a fight with inmates, pacing across a hard floor, sweat dripping down your face while exercising in the cell, turning your face to sunlight coming through a high window, leaning against the bars, hooking your arms through the bars, the chafe of handcuffs or ankle cuffs, uncomfortable shoes rubbing at feet
--The words you choose can convey atmosphere and mood.
I pull down Jackie's picture from the gloomy wall next to the bed, careful to only touch the edges. She's in the park near our old place, apples in her cheeks as she pumps her legs on the swings. Her grin is so bright I smile just looking at it, and I long to touch her face, but fear wearing away her beautiful image. In the photo she's five or six, an age left behind a dozen years ago. I wonder what she looks like now, if she's happy. I would trade another year in this place of cold steel and weeping concrete to have just one hour back with her, there in the park, where our smiles could meet without a photo between us.
One of the guards waited for me outside the cell as I glanced around one last time at the barren walls that had housed me for seven years. The room was straightened, toothpaste scum washed down the cracked sink, table cleared off, bed neatly made. I didn't need to do any of these things, but habits are hard to break. In my hands, I carried three items: a copy of Orwell's 1984, a photo of my wife and our son, and my toothbrush. Maybe it was stupid to bring the toothbrush, but I couldn't bare to leave anything personal of myself behind in a place that held only frustration and despair. I turned my back on the room and follow the guard to where my family waits. A strange feeling swelled in my chest, something absent so long I almost didn't recognize it: hope.
--Similes and metaphors create strong imagery when used sparingly.
Example 1: (Simile)
The bed creaked as I sat, the lumpy mattress sagging in the middle like the sludgy bilge of a rotten ship. How many others had claimed this spot before me, staring at the same chipped paint that I now did?
Example 2: (Metaphor)
As the metal bars rattle close behind me, my eyes grow used to the dim light of my new home. Slowly they reveal themselves to me, the ghosts who have remained to greet the newest inductee. Carved and penned, the walls are filled with ravings at the unfairness, the wasted opportunities. The dingy cement reeks of loss, tattooed with the life stolen by steel and fences.
A special note:
I found some good information here regarding prison life: contents found in a prison, items that can be purchased by prisoners and their costs, etc. There are also personal stories regarding inmate treatment and the gritty reality of prisons. As this information is provided mostly by inmates in Pennsylvania, be aware that some of the language and content may be highly offensive.
Keep in mind too that not all prisons or operations are similar nor host the same conditions or environments, but some of this may offer good generalities for fiction writing.