The "Barrens" are not one homologous thing. Basically, "Barrens" are areas without meaningful police coverage or other regular government services. The exact nature of those areas varies greatly. Some areas, such as Troustville in Redmond or Loveland in Puyallup are basically just vice and nightlife districts. May of the residents actually have jobs (bartenders, cooks, dancers, bouncers, musicians) or illegal jobs (sex workers and other vice related things), and those folks have some cred to spend on daily meals and soycaf and the occasional clean set of underwear, so here are a whole secondary set of small (often very small) businesses to supply those needs. As for the look, I really like what comes across in the Shadowrun Returns games. The whole place has an ad hoc and improvised feel to it, bit its still actually a neighborhood, people live there, have business there, and do what they can to get by there.
Other parts of the barrens are slum housing, like Bargain Basement in Redmond. Cracker box sized appartments with a bathroom down the hall or out back, no kitchen except a hot plate or electric kettle. Keep in mind, however, that people can't just sit in room and feel bad 24 hours a day. All of those people need potable water and a meal or two each day. Some of these people have SINs or fake SINs and get some welfare or disability, others are scroungers, heading out into the city each day look for scrap, usable/sell-able garbage, and to commit petty crimes like shoplifting or muggings. The alpha dogs of these areas are the gangers, who engage in more organized and profitable crimes like drug and btl traffic. Again, people here need socks, noodles, and a water filter, so there would be street markets that take barter, corp script, and have a nuyen to market chit exchange.
Really nasty areas (Glow City, The Rat's Nest) are basically something out of Road Warrior or one of the Fallout Games.
And also note, there are some areas in the "Barrens" districts that rise above squatter lifestyle. Puyallup City proper actually has a working city hall and business area. The outlying trailer parks I imagine get pretty scarry, but there is actually legitimate (if low) neighborhoods there. There is probably police and emergency services coverage, even if most of the rest of the district doesn't get it.
