For Commodities, I use PDBC (Invesco Optimized Yield Diversified Commodity Strategy ETF) as my preferred vehicle in the test portfolios, and also hold it in real life. Features: largest "broad basket" commodity fund, decent expense ratio, high dividends. Better for tax-advantaged accounts.
Fund Home Page:
Barchart Page:
The Basics:
PDBC is my choice to represent the commodities asset class, though it does have some peculiar aspects which may not make it fit for all RP investors. On the plus side, it is the largest of the diversified, broad commodity ETFs, with an AUM almost double that of the second-place in this category, FTGC, and is managed by one of the leaders in the commodity ETF space, Invesco. It has had good performance in 2021/2022, a time of high inflation, and so it has performed as advertised as an asset to do well in this economic environment.
At the same time, it may not be for all RP investors. For one, the "optimized yield" part of the name is a way of saying that it outputs most of its profit in the form of dividends, and its success will not be captured as much by a rising share price. Imagine a commodities fund makes a profit on its future contracts. It then has two options: pay that back to shareholders or increase purchases of future contracts – this follows the first strategy.
PDBC's approach can make a quick analysis misleading. If you focus on the share price only, you'll miss the substantial income it generates. For example, PDBC's  52-week change is down 8%, meanwhile every other commodities fund seems to be up 20, 30 or 40%. The rest of the story is that PDBC paid out $7.147 in dividends last December, so with that included, it is actually up 37.6% over the past 52 weeks.
As such, it is NOT tax efficient and is best suited for tax-advantaged accounts. In real life, that is how I hold PDBC, and for the test portfolios, dividends are tracked, so their success is accounted for. If, however, investors are looking for a commodities fund for regular brokerage accounts, PDBC is not likely the best option (see below).
A second reason that PDBC is not a great fund for everybody is its mix of commodities. It holds fourteen different commodities (fewer than some others) and is more tilted towards industrial metals (base metals) than most, with less allocated precious metals. Here is the breakdown for PDBC (as of March 2022):
Some other commodity funds can be much higher in gold, sometimes 20 or 30%. This means that if you use PDBC, you might want to have an additional allocation to gold, and not use PDBC as a way to get exposure to gold. Yes, there's a little, but not very much. In this case, perhaps COM would be better (27% gold, plus 13.5% in silver).
PDBC's expense ratio is .59%, quite high compared to most of the index funds used in the test portfolios, but much more of a typical number for commodity funds. Cheaper options do exist, however. Lastly, with just fourteen commodities, it is not as broad as many others (BCI has 23, for example). That could matter for diversification (I need to test this more).
Correlation with Other Assets:
The main goal for commodities is to be a source of returns that will: 1) be a source of return in times of high inflation; 2) as such, not be correlated with stocks or bonds. As for the first, the recent months of high inflation and surging commodity returns does suggest it is accomplishing this goal.
To turn to the second, I ran a correlation matrix on Portfolio Visualizer (link here). The returns date back to December, 2014, so not that long a timeframe. The numbers came in a little higher than I expected – this may be because of the time frame, or the recent performance. Anyway, it is still only weakly correlated with equities, negatively correlated with bonds, and then as random as gold.
Other Options:
As mentioned, PDBC has some peculiarities that make it not suited for other investors, and this is a case where people starting or transitioning to a RP-inspired portfolio might want to put in some extra research.
If holding commodities in a taxable account, the funds GSG and DJP had dividend rates of 0% and have very high 52-week returns, leading me to guess that they are using their profits from futures contracts differently than PDBC (more research is needed). BCI and BCD are two funds with  lower expenses ratios, at .25% and .29%, respectively. If you are interested in a mutual fund, the DFA Commodity Strategy Portfolio (DCMSX) caught my eye since its a DFA fund.
Meanwhile, if you're keen, here is a link for my search of "Broad Commodity Index" funds using the ETF Finder on Barchart: