What products would you put in a Dungeons and Dragons hobby store for teens-adults?

If a product is trademarked you need a license to sell it.

Your retail outlet may not need a specific license from Sword Coasts, but the distributor you bought the merchandise from would have to have one in that case.

Clearly D&D merchandise would be your number one priority. Aside from that, refreshments such as soft drinks and cheese balls would probably be a welcome addition. Cheese balls do leave a residue on the fingers. Moist towelettes could prove handy as well. This works out well since cheese balls are indeed tasty and irresistible. Most customers would not want orange fingerprints on their brand new D&D gear, so, capitalize on that by selling the towelettes. I wouldn’t discount the notion of rabbits feet. A little luck never hurt anyone. Carry some convenience items such as automotive fuses and deodorant.

An area set up for role playing the game would probably help get people in the store.

Screw cheese balls. Funyons are the gaming fuel of choice.

Also:
Other games.
Modules.
A used section would be awesome, so you can keep old versions of the rulebooks and their related modules in house for us old-school nerds.
Beautiful dice sets.
Dice bags/boxes
Miniatures for the people who use them.
Oh, and did I mention other games? D&D players aren’t plentiful enough to keep your store open. You’ll do better as a generic geek haven.

My #1 recommendation is plenty of table space for players to play on.

My favorite game store hosts a different group every night: Mondays are family-friendly board games, Tuesdays are Pathfinder, Wednesdays are D&D 4e, Thursdays are Dresden Files RPG, Fridays are varied (Shadowrun, Cthulu, etc.) and Saturdays are for Magic the Gathering. I think it is good to appeal to a variety of people.

Nice for D&D:
dice, dice bags, books, tokens, miniatures, tiles, mats (super handy)

Nice for a store:
They host a class every Saturday on how to paint miniatures and give a discount on paint. They have a printer and will print off a character sheet for you, or other small things you might need. DM’s get a free drink each gaming session

They have plenty of food available: sandwiches, soft drinks (including rare items like bundaberg ginger beer), sports drinks, chips, pretzels, etc. (cheese balls would drive me crazy and I’d go somewhere else)

From experience: The D&D culture is severely lacking female participants, and the boys really do WANT real girls participating.

You know, the prime readership of vampire and fantasy novels is female.

It seems like a fusion, ready to happen!

Market to the girls who crave the fantasy life. “Seeking strong female warriors to join league. Free Mtn Dew and Doritos”

Are you only selling D&D? Wizards of the Coast has tons of other products, just sell all of them. Buy and sell single collectible cards too. Also branch out to other games of all kinds if you have room. Make sure to offer plenty of accessories (storage boxes, card sleeves, card protectors, dice, dice bags/boxes, tokens & counters, playmats, etc).

Pathfinder. ;) d20 products, or any other more indie game system that focuses on fun, and not forced buys.
WOTC (Hasbro) did a good job of reviving itself after TSR was letting it rot, and then promptly shot itself in the foot. White Wolf did good with the WOD and then shot itself in the foot with the nWOD. They do something right and then turn around and say, “Wait a second! We did something right?! We’ll fix that….” Two popular franchises virtually flushed down the toilet. White Wolf is even bringing back The Masquerade because that is what people liked and were interested in, not a watered down rehash. 4E D&D Tiefling PC’s??? OMG…. How World of Warcraftian that was, uhck… On par with Marvel Comics making Jubilee a vampire because the Twilight movies were popular with people wearing training bras. Just need to update the game mechanics and quit trying to reinvent the wheel.

The great thing about roleplaying games, is that you don’t have to follow all of the rules everyone else does. As long as the rules you use work for the group you are playing with, no need to add or change anything.

I’d have a few dozen copies of The Pickup Artist on the shelves.