Americans continue to accumulate more toys, furniture, and knickknacks than they know what do with. For proof, look no further than the growth in the self-storage industry. Although the pace of growth may be modulating, self-storage rentals have been one of the fastest-growing pockets of the real estate industry over the past 40 years. There are now about 50,000 self-storage facilities in the U.S., and one in 10 Americans has resorted to storing possessions offsite.

Judging from the many portfolios I review during Morningstar's annual Portfolio Makeover Week, many investors have a similar glut of "stuff" in their portfolios. For every single portfolio I receive that's whippet-thin--without an excess stock, fund, or ETF to spare--I come across 10 more that have 50, 60, or even 100 individual holdings.