I'm a bit behind here ...
Day 1 - Yep, the Fighting Fantasy gamebooks - I think the first was the Tower of Destruction - I got to face off against and banish a daemon prince with a magical ice-sword!
Day 2 - A blurry memory, I think it was possibly Aeon Trinity with a friend of mine over a weekend, but we both had characters and the role of GM was shared.
Day 3 - Again I'm not sure. Possibly Tunnles and Trolls - from a second hand bookstore in the sleeply town of Holmfirth (The Hollywood of Yorkshire). I don't think I bought and Fighting Fantasy gamebooks for years - my local libraries were always well stocked - but I did buy Dungeoneer, Out of the Pit and Titan around that time too (good times...).
Day 4 - Paranoia through Bundle of Holding - plenty of enlightening GM tips there