Hi and welcome, mrgimmick! That's one impressive collection, there. The leather backpacks are rare on this side of the pond (to my knowledge, only one or two were given away by magazines as prizes here, in fact).
If it's of any help, I know of;
Two more backpacks (there's the one given away with the purchase of the Microsoft Windows 95 port of the original game at the British chain Dixons, which is the one I have - it's dark green canvas with black nylon straps, with an embroidery of the Croc: Legend of the Gobbos logo, and the famous image of Croc holding a Gobbo; There's also a more cheaply-made one that promoted Croc 2 in the UK, which simply had a screen-print of the Croc 2 logo with the Croc-running-with-a-crystal-under-one-arm picture on it; It was often sent out as part of a prize pack containing some or all of the watch, CD wallet, and frisbee listed below)
A Croc 2 analogue watch
Croc 2 CD wallet
Croc 2 frisbee (these were quite common, to the point that some folks started making them into clocks, instead)
A sheet of Croc 2 magnets, a US-only item
The poster from the packaging for "Croc" for the Game Boy Colour
A black Croc: Legend of the Gobbos baseball jacket, with brown suede arms, an embroidery of the Croc: Legend of the Gobbos logo on one side of the chest on the front, and a huge Croc applique covering the back (this seems to have been a UK item given to Fox Interactive staff - that's how I obtained one)
The CD wallet made to promote the UK "Platinum" £19.99 budget release of the original game, which features the Croc: Legend of the Gobbos logo screen-printed in black on a silver leatherette case
The life-size four-foot-tall plush that was given away in a US-only online sweepstakes promotion for Croc 2 (this is how we know what Croc's height is supposed to be, incidentally), which was run on Fox Interactive's website back in 1999 (the winner won the plush and a family vacation to Australia)
And the wooden "?" box, containing a crystal with the Croc: Legend of the Gobbos logo set into its base, with an invite to the ECTS 1997 press party for the original game's launch etched into the lid (I was given the last one of these by a lovely Fox Interactive UK representative, who I corresponded with several times over the years back then, and then later got to meet in person when I was one of the winners of a trip to Argonaut Software Ltd. in 1999).
You already mentioned
the plush (of which I believe there are fewer than ten in the UK - seven were given to those who won the trip to Argonaut, and at least a couple more were given away by magazines to promote Croc 2's launch; More of the plushes exist in the US, where they were used to promote the first game rather than the second, but I don't know how many - I would guess more than there are over here), and a few other items, and I think that our posts combined cover most of what I know to exist.
When I visited Argonaut in 1999 (it was part of a promotion for Croc 2, where the winners got to see the game being worked on, play-test a release candidate version* that was due to be sent off for approval the next day - which had some big textual differences to the final game, in that it was written in proper English and was full of British colloquialisms, instead of the toddler-style text that ended up in the final game - and, of course, take a tour of the studio and meet the team), I was told that there was believed to have been a set of plastic figures made to promote the first game in what they recalled as being the US, at Toys 'R' Us branches, but I have never been able to find such a thing in all the years since then. I don't know for sure, but it's possible that these could have been prototyped and approved, but then never mass-produced. If you can find these, or even any evidence of them, more power to you!
*I was, to my knowledge, the first member of the public to play Croc 2. I am proud of this.
(Also, one of the bugs that was spotted by someone that day remained in the game - in the snowy stage where a Gobbo woodcutter chops down a tree, the woodcutter will flicker and become invisible a couple of times. It always reminds me of that trip. Thankfully, the horrible snow-head level was fixed, though.)
There is one more thing that remains a grail: There was a TV series pilot made by Saban in 1999, but it was never aired anywhere. It got a mention in at least one British magazine (at around the same time as the Rayman television series was in production for its first airing in Canada, if memory serves), and the guys at Argonaut had either seen it, or had input on its production (they spoke about it during my visit). I was unable to obtain any more information on what had happened to it when I contacted Saban about five years or so ago, however. Again, if you can find this, more power to you - I suspect it would be next to impossible.
If I can be of any further help with your list, please let me know.