Mostly combat-formations, history, and period attire (including any unstated inconveniences they provide).

Oh, and popular science articles and discussions of speculative-fiction.

Slight chances I may even be googling specific procedures of little relevance to my normal day... like how to prep a Baulton-Paul Defiant for battle and the finer points of precision dive-bombing.

And then, very rarely, do I look up popular animes and such on TvTropes.