42. As many DP subscriptions as 50K will afford him, to help the circulation numbers. (Especially helpful around the time Lex was buying the "failing" paper.)
There, that's not really an investment per se...
43. A very large stock of Twinkies, Ho-hos, Ding-dongs, and Snickers...all of his favorites. (According to Jonathan in LOTF.) Oh, and plain-cake donuts.