OK, I know the books...the card-game was a trading card game, wasn't it?
It was, from a company called Mag Force 7 and released between WC3 and WC4. There was a 300-odd card base set and two promo cards.
Does anyone have more detailed information on the other stuff (clothing etc.)?
In terms of merchandise sold to the general public:
There was a Wing Commander hat sold by Origin when the original game came out. It's a black hat with the original game's logo on it.
When Wing Commander IV came out there was a line of merchandise from a company called Zanart. There was a little advertisement for it all in the Wing Commander IV box (a little glossy red fold-out paper). They sold two hats (the WC3 and WC4 logos), four shirts (WC3 box art, WC4 box art, Excalibur flying away from Kilrah and Dragon landing at Telamon) and four pieces of "Chrome Art" (matted and optionally framed versions of the same art as the shirts that were printed with chrome parts so they're shiny).
Then there were a number of things produced for the movie: a Kilrathi mask and helmet, a 'Pilgrim Cross' knife replica, an official movie magazine and a series of action figures.
There are also two other levels of merchandise out there--promotional items (created for trade shows, given out by sales reps, etc.) and team items.
In the former, there's everything in the universe, from Wing Commander IV branded binder-bags to flavored water with the Wing Commander Prophecy logo on it! There are lots of shirts, jackets, hats, etc. of different designs out there.
Then there's stuff that was given to Wing Commander development team members--each game usually had a 'team shirt' and many had patches (and the main series' had leather jackets).
Original Wing3 release featured a tin can with a "making of" included I believe. And Kilrathi Saga contained a T-shirt, And I beleive that from the cardgame you got one card included with either WingIV or KS. WC1 seemed to include an origin cap?.
No shirt with Kilrathi Saga. There were two 'tin can' versions of WC3--one that was sold by EA direct (that had more stuff) and one sold at "Sam's Club" stores that had a cooler box. They did come with an ugly, ugly shirt (and I believe the German version comes with a different and somehow uglier /white/ shirt).
Oh, music CDs are another thing--there was a Prophecy soundtrack and then a good dozen-or-so promotional CDs that had WC music over the years.