Surprise: the movies and TV series all have it wrong. There's no one, defining culture in prison, and the differences between one unit and the next — even within the same facility — can be substantial.
A standard set of policies governs the Missouri Department of Corrections. Every one of the sixteen institutions within the Department have to abide by those, with a little wiggle room in the form of their own Standard Operating Procedure (which is nominally for clarification but is mainly used by prison administrations to deviate from the letter of departmental policy). SOP is where the details lie.
The DOC might allow its residents to mail order a certain type of art supply material, but if one maximum-security facility decides not to allow that item — say, tunes of acrylic paint — they're within their right to impose an SOP that clips a prisoner's creative wings. Case in point was Crossroads Correctional Center, where I spent nearly seventeen years and never was allowed to order paper or colored pencils. My first month at ERDCC, I remedied that. Today I have several types, colors, and sizes of paper stock, as well as charcoal, water-soluble graphite, and watercolor pencils. Other maximum-security facilities let prisoners order craft glue, needlepoint supplies, et cetera. The decision to allow or restrict such things seems to be the wardens' discretion.
Top-down policies are one thing, but grassroots factors, arguably, have even greater effects on prison culture. After all, policies are enforced (or not) and followed (or not) by people. All it takes is one indifferent or ignorant guard and one unaware or brazen prisoner to dissolve any rule.
Then there are the unwritten rules. This is where culture, aka "how we do things here" comes in. In prison — in this prison, anyway — there's a taboo against spitting in the sink. When you're brushing your teeth, the expectation is generally to spit in the toilet. Why? I don't actually know. Because germs, I guess. They say, "When in Rome...," but my current cellmate and I refuse to conform to what we think is a silly custom. We still spit in our sink and clean it regularly, just like regular people do.
This makes us a minority, and there are plenty of other circumstances and conditions in which a status quo defines how everyone behaves. Different areas of a single housing unit can often vary in their customs. Here in B-Wing of Housing Unit 6, one of the places where a lot of people hang their laundry after washing it by hand is on the mesh underside of the stairs (never mind the filth that rains down from shoes as people ascend and descend). I've never seen people hang their stuff under the stairs in any other wing I've inhabited, yet here it's the norm.
Or take the practice of someone hanging their ID card on a shower when they come in from recreation, thereby calling "dibs" on it while they gather their shower supplies. In some wings, the reservation is honored, even encouraged, while in others it could end you up in a fight.
Consider, also, the segregation of telephones into whites-only and blacks-only phones. Here we are in the twenty-first century, but some members of the institution's population want everyone sharply divided in accord with racist ideals. In some wings at this facility (not mine, thank goodness) this practice is considered acceptable, even normal.
These differences aren't always negative. I've known wings that have a new-arrivals welcoming committee offering a little package of snacks and inexpensive hygiene products. I've heard of places where a whole wing will get together, one night a month, and prepare a meal. Sometimes you'll hear about a unit where residents periodically band together and deep-clean the place, where discourtesies are not permitted, or where there's some sort of self-organized game competition, complete with prizes.
It's always interesting to hear accounts of how things are at other facilities. A couple of years ago, the Missouri DOC cut off communication between prisoners at different camps. They never outright said why, but this practice of barring prisoner communication mirrors rules that other states have in effect. We don't hear much about customs in other institutions, except when someone transfers from elsewhere. Then it's like story time.