The Stuff in question can be anything from a wooden three-prong fork to a camping bed to a hanging candelier to the canvas pavilion to put it all in. So here's an overview of the SCAdian merchants I frequent who have on-line resources:
For feast gear and the basic necessities of life (everything from candles to tunics to trim to shoes), all at very reasonable prices, you can't beat the Pillaged Village.
Won an award and want a medallion to show it? Doing a job and want folks to recognize you? Drachenstein Treasures has beautiful cast, hand-enameled medallions for officers, peers, and kingdom-level awards. I have several of their medallions and have been very satisfied.
Looking for a source for pavilions? Our entire encampment is housed in Panther Pavilions. We love them, and they've kept us warm dry and well-housed during a decade of wind and weather. Pavilions are also available from Tentsmiths, Four Seasons Tentmasters, and Dragonwing Medieval Pavillions and Tents.
Do It Yourself -- Whatever It Is!
Finally, a frequent answer to "where do you get your stuff" is, I MADE IT -- and so can you!
Interested in making your own pavilion? Check out these Medieval Pavillion Resources. Other sources for information are Plausibly Medieval Pavillions, and there's even a source for those who want to make an AngloSaxon Geteld. Finally, check out Cariadoc's Miscellany, on Building a Conjecturally Period Pavillion.
It's relatively easy to make your own accessories as well. For example, for those of you who came looking for a picture on how to make a decorated leine pin, here is a very quick & dirty sketch:
