I google the nearest bar to wait out the time with a pint or 3.
Bookshops, of course, especially used bookshops.
When I’m in another part of the U.S., I can enjoy grocery stores and supermarkets, just to see how the local tastes differ from those in my hometown.
People in North Dakota seem to like their jar pepperoncini flavored with garlic and dill!
Fry’s Electronics
Marijuana dispensaries.
I love to wander around in Antique Collectives. I already have way too many souvenirs, kitschy tchotchkes and gewgaws so I never buy anything–but I will take pictures of stuff that catches my eye.
I’ll go local.
Buckdancer’s, a local music store, as in instruments. They let you play anything you want. there’s always an amp hooked up and you can just grab a guitar off the wall, sit down, plug in and make some noise. Or you can play a $3,000 Martin in the acoustic room. They do repairs, lessons, a guy who used to work there is producing my band’s EP … it’s a cool place.
Bullmoose Music, a local music/book/movie/video game store. Actually, I’m not sure just how local it is. There are two locations that I know of. I don’t know how much of a franchise it is.
ETA: I see **CoastalMaineiac **calls it a “Maine chain.” I’ll go with that.
First choice is any gun shop/tackle shop. Small mom&pop style more than say a Dick’s or Cabela’s.
Second is Tractor Supply or possibly Harbor Freight depending on location.
Thirding Fry’s Electronics. You could lock me up in there for a year and I wouldn’t mind.
You need to git yo’ bad se’f to a college town. They have used bookstores and used record stores and used cheapo clothing stores.
I can get lost in any hardware store, but for the best putzing, I’m close to two Half-Price Books. I have to set an alarm before I walk in, because otherwise I’ll be an hour late for my next event. Due to the combination of new books, used books, comics, LPs/CDs/DVDs, games, audiobooks and [cue heavenly choir] Clearance Items.
It’s a chain, with 120 stores… hope there’s one nearby. And you have a spare hour.
Kittery Trading Post, a sporting goods store in Kittery Maine, about 10 minutes from home
Bookstores, hands-down. Video/electronics stores after that, I suppose.
After that, it’d have to be places selling something relatively novel. Skeletons, Scottish themed items, hardware salvage, military surplus, scientific supplies, movie props…anything I’m at least tangentially interested in, but can’t find normally or in high concentration in a regular department store.
Things just haven’t been the same since The Nature Company went under. 
Bookmarked the site. Next time I run up towards Saco, I may just have to plan a side trip. The stock of frontstuffers isn’t the greatest but I have a Plan B for when I travel outside of my state.
Went to the movies today at a theater that requires me to get off the train in the station underneath Nordstrom, which was the perfect excuse to spend some time in the shoe department. That would be my #1 stop for just checking out the merchandise.
#2 would be any of the 9000* Walgreens located near my home or work. I have been known to take a meandering walk that lets me putz around in five different Walgreens on my way home.
*O.K., I admit this is an exaggeration. There are apparently only 17 Walgreens within my general vicinity.
T. J. Maxx and their Home Goods spinoff.
I can find something interesting in any store near me
Ayers, a modern-day equivalent of a five & dime. See for yourself.
Home supplies, be they high end or dollar store.
Half an hour is barely enough time to enter it, but right now I work across from an IKEA…
I’m rarely in this position because the only times I seem to just be hanging out in waiting mode is an airport or railway station.
But if I’ve got time to kill before a show, I’ll hit up Foyles, since it’s one of the few places that’s open after 6pm that isn’t a pub or restaurant.
Super rainy day with no plans but a bit of cabin fever, and don’t want to bother with the crush of museums and high street shops, I’ll hit up several second hand clothing stores in Notting Hill.
Foyles, for those who don’t know, is a British bookstore chain with seven stores.
~Supermarkets (can’t help it, it’s a byproduct of working in the industry – gotta check out the competition)
~Kitchenware stores, especially wholesalers who sell direct to the industry like Restaurant Depot.
~Liquidation stores – they’re maybe a step or two above dollar stores and have an ever changing inventory. There’s one called the Job Lot which is roughly a mile from our house. I wander around there every so often if I don’t feel like driving anywhere. There’s a larger one a few miles away I’ll go to if I’m still feeling restless.
~ Any bookstore