A few friends and I are going to draft the heck out of the winter block in the next few days. After looking at Tzumain's site, specifically an article on drafting, there was mention of an ITE draft supplement that was used alongside the draft pack (I think it was 2 plots, a conscriptor for each house, and a few locations). Since we never saw any place selling these supplement packs, we just made our own from our own card libraries.

My question is, if we were to do the same for a winter block draft, what cards should we use as a supplement to the draft pack, if anything?

The same ones. Those draft supplements (which were never sold as a separate product) were put out to get to 7 plots and to replace the income locations with things that had influence.