My contribution may be too late, ontarioice. but in case you do check back on this post, this is my experience.
I do the DT General Knowledge each Saturday and Monday. I don't have half the intelligence or the experience of some of the regular Q&P puzzlers, but although I have a raft of reference books I hardly ever use one. I almost always find the answer I need on Google or a missing letters program. The one indispensible aid is a good atlas - a very old one is useful as well as a modern one!
Best wishes, A/g.