OK, here goes. This is still being built on but this should whet your appetite!!:
Creation Motorsport will donate a visit for two people to their garage during the 24 hour race to experience what it's like during the actual race, including being in there during a pit stop. This is something that is just not normally available to the paying public!
Creation will also donate some team shirts or t-shirts which will be signed by the drivers.
Creation have written to all their drivers and any other driver they know to ask for individual donations.
Darren Turner will donate "something" but he doesn't know what yet as he hasn't been given his Team kit yet. I am to meet him there to collect "something"
Chamberlain Synergy will donate a Wishbone off their LMP1, signed by all three drivers.
Amanda Stretton (Chamberlain Driver and TV Presenter) will donate a signed set of her race overalls.
An ex Le Mans driver who now races in the Radical series that supports LMS in Europe has stated that at his next practice day at either Brands, Silverstone or Donnington (TBC), he will take the winning bidder out for 5 laps as a passenger in a Radical SR5. (Out lap, 3 Hot laps and In lap)
I'm not sure if "the wheel" has been mentioned on here yet either.
At Sebring, CA'ers obtained a wheel off the Sebring winning Corvette GT1 car (used in qualifying, not in the race) was signed by all 6 Corvette drivers and was donated. (Have we collected it from Barwell yet?)
Chris Hall has also obtained lots of additional items items. As per his posts on DfH:
Signed Avon Tyres Limited Edition Cap, by Bradley Ellis and Alex Mortimer, the 2007 British GT Champions.
There's also a signed Rockingham poster, signed by about 12 BGT drivers, including Alan Simonsen, Cocker and Drayson.
All have been autographed in thick gold or silver pen.
"From Team RPM, 2007 British GT Champions Bradley Ellis and Alex Mortimer have donated a signed, limited edition Avon Tyres baseball cap in addition a Rockingham BGT Poster autographed by a host of drivers, including Allan Simonsen, Jonny Cocker, Tom Ferrier and Adam Wilcox is up for grabs."As a bonus, I have a signed CR Scuderia t-shirt, autographed by Kirkaldy, Mullen, Rob Bell and someone else...

I got Oliver Morley and Tom Ferrier to sign a Lamborghini team hat for the auction.
I spoke to Modena, they have a book on their history coming out soon, and if it's ready in time they'll donate a copy signed by their drivers - if it's not ready, they agreed to rustle something else up.
The British GT (SRO) have donated one of their standard goodie bags and I'm now trying to get a free ticket/grid walk as well .