I don't own any free gifts of any old comics before about 2007/2008 (or thereabouts), but one thing I do have is a Plug Sports and Social Club Badge.
This badge was given away when you signed up for the Sports and Social club in Plug comic. I don't actually own any issues of Plug, but here's an image I've "borrowed" from Twoheaded Thingies.
And that's the only free gift I have from before '07. If free gifts interest you, Lew Stringer wrote a fantastic series of blog posts over on his now defunct blog Blimey, which starts here and comes in seven (I think) parts: