Also of note:Though you -can- sell to the Trading Post near Clownsteady, Telbooze, Bark, The Trading Post at Black Scratch, and the Trading Post at Skinner's Roam, they don't have a dedicated Trade merchant that allows you to buy all of the trade goods. Sometimes they'll have a few trade goods to sell though.
To those with the strength to carry in bulk, Trade goods are a great way of raising a lot of money which can be auxiliary to whatever else you happen to be doing at the time, or can be focused on to gather vast wealth quickly.
Starting off you wont have the strength to move much very quickly, but you can build up strength quickly by loading up a back pack then de-equipping it. Sense a full back pack in your inventory proper will put the full weight of everything inside on your character you'll get heavily encumbered, and the heavier your load, the faster your strength grows. You can expedite things further by picking up a fallen bandit or a team mate to give yourself an even heavier load.
Each trade good (except Medical Supplies and Narcotics *cough*) has a very distinct look to it, which makes it easy to identify in shops. You buy them from Trade shops (Which are buildings with a sign that says TRADE on it.) Trade shops are very important because currently they're the only shops that will allow item stacking. Items will stack to 5 in Trade shops so long as they are the same basic items; this includes trade goods, armors, and weapons of the same type and make. (i.e. Short katanas that are Manufactured by truth and are Mk II will stack with others of the same build, but not Mk III's or General Metal Model 2's)
Trade goods buy and sell from at the same price from the same vendor, so if you accidentally buy an item marked up by 120%, you can sell it back without a loss of money. This does not hold true for equipment, however, so keep that in mind.
Every town will have it's own prices for all the trade items, which will alter the price by a percent. Building materials could sell at Brink for 80% their standard price, but could sell at Trader's Edge for 116% standard price. This means that buying from brink and selling at TE will net a hefty 36% of the item's base price in profit! Paying attention to both the discounted and the marked up items is very important if you want to make money trading.
Below are the items that you can buy from a trade goods store. You can sell these items at any store, but it's best to try to sell it to a trader where it will stack in the shop keeps bags, allowing you to pawn off more before their bags fill.
Textiles: 2x3 Grey textured box with a brown band. Base Price: 50

Steel Bars: 1x6 Grey metal bar. Base Price: 80

Food: 3x5 Large Grey Wooden crate. Base Price: 100

Tools: 3x2 Tall olive green box with two holes on top and bottom. Base Price: 120

Luxury Goods: 2x3 Grey Box with dark grey x patterns on it. Base Price: 300

Robotic Components:2x4 Red and grey metal box with 6 holes/bolts in it. Base Price400

Rum: 4x3 Brown Bottle, Labeled as Rum. Base Price: 400

Medical Supplies: 3x5 Olive Green Drab box with white and red stripes in diagonals. Base price: 200
Narcotics: 3x5 Looks Extremely close to Medical supplies. Base Price: 800

(Top is med, bottom is narc)
Building supplies: 3x6 Large Metal box. Your best friend. Base Price: 500

But that's not all, the med kits also act like trade goods, though you they're not sold in stacks at trade goods stores. They come in Basic (1x2), Standard (2x2), and Advanced (3x3). They aren't really all that expensive (At 40, 100, and 200 respectively)

Sometimes you'll get a town with very high buy values for everything. This can be a blessing and a curse, as you can make a tidy profit from selling to them. However -you can run them out of money-. Sense you'll be selling them things but wont be buying things back, you it's possible to burn through their finite amount of money. You'll know you hit this point when you try to sell them something and get a "You don't have enough money" error. If you start an import game, you'll refill their coffers, but that can get annoying.
At current there is no real noticeable difference in the spawning of hostiles dependent on where you are on the map, as such a good trade route is a short route that's easy (for you) to navigate where as many stops as possible have a trading goods shop. My route is pictured below.

Running a route like this will tend to result in 3~8 hostile encounters a loop, which you can use to snatch up swords and the like to pawn, or ignore then if you don't want to budget for 2x8 weapons that only tend to sell for about 200.
Alternatively, you might get lucky and have two towns close to each other which have a good trade off of goods, like one shop selling lots of things cheep and buying Medicals and Narcotics for expensive and a near by town doing the opposite. This can lead to very short trade routes which get very profitable.
Sense shop prices are randomized, I can't simply provide you with a handy chart of buy-here-sell-there, but I would suggest taking the time to buy one of every trade item, stuff them in a pack on a character who's strong, and traveling the world to check values for items. It's very time intensive, but very profitable.
Please let me know if there's any more information you'd like me to add to this guide, or if there are any bits of misinformation so I can clean them up. Thanks and happy desolate wasteland trails!