stocks - for prosperity
bonds - for deflation
cash - for recession
gold - for inflation
The Browne notion is that is impossible to predict/guess financial market events with any consistent skill, so it's better to have non-correlated assets that perform well as a total portfolio. Eg in the 1970s when stocks & bonds both declined, gold went up.
Supposedly since 1970s this portfolio has performed similar to an 100% stock portfolio, with the worst year being down ~15%, while stocks have been down ~50% at times.
craigr's Crawling Road blog & discussion forum - many knowledgable gurus on here, veteran HBPP personal investors
UKer Clive/JF from crawlingroad forum site. Clive advocates for currency diversification, to hedge against domestic currency collapse. This is contra US "convential wisdom" that USD is somehow forever safe, & anything international is riskier, stupidly conflating stable rich countries like Canada or Germany or Japan (which might be safer than the US, at least for some years) with unstable countries like Argentina or Pakistan. This is also contra Harry Browne's own thoughts, of having 75% of the PP in USD-priced assets & 25% in gold.
US economic problems such as a trade deficit, budget deficit, unwillingness to cut profligate cartels such as the Military Industrial Complex. Also, many key assets such as oil & derivates being priced mostly in USD. Maybe in the future only 50% of oil will be priced in USD. Either of these issues could make it hard for the USD to get much stronger, with much risk of it getting weaker.
It seems that diversifying among global currencies would be "safer" than holding assets exclusively against any 1 currency.
Belgian Marc De Mesel, who like Clive shows (an extreme) example of domestic currency risk, with the 2008 Iceland PP
Boglehead's HBPP forum page
8 Lazy ETF portfolio reviews, which includes HBPP
Get Rich Slowly review