I beat the monk in the tavern and got the "Lucky Roll!" entry in my journal and it tells me to go to the "Extras" section of the Main Menu. In there, I still only see credits.

Is this a bug or is there something else hidden I'm missing?

It's a little easter egg, or shameless plug, or however else the young'uns call it these days.

http://www.gog.com/en/forum/general/extra_prize_in_witcher_2

Your gaming prowess has netted you real-life benefits. I feel like I'm in Omikron: The Nomad Soul all over again.