Good input above, but my first reaction to this post's title was on the expense side rather than investment. Now I never did the careful analysis and selection of Big ERNs withdrawal rates...so far in my second year of ER, I've just been bumping my budget by approximately inflation. The problem is, the official inflation rate is built off of a selection of goods which....do not necessarily represent the selection of goods (especially nowadays) that the average person buys. I'd read this before, some study of how much a typical consumer budget's inflation does not track the official inflation rate, and is usually much higher, because the things in each basket are pretty widely divergent.
Even for FIRE folks, our budgets may diverge a lot, too. I know my budget diverges a lot given the proportion allocated to travel and health care. Two things that absolutely do not stick near the official inflation rate. Luckily, travel is very discretionary and by the time I'm 90 I might not be able to spend a lot on it anyway, so won't mind it having been significantly devalued. But healthcare certainly worries me. In fact, I have significantly overbudgeted my health care category early in my ER in order to avoid ruinous devaluation/ inflation I can't keep up with. It makes my budget now a bit artificial, and I have carryovers of one time money each year that I'm still deciding how to most effectively handle, but it's important to me not to have to worry about how I'm going to take my budget from like $500 per year to $20k per year in a few decades only growing my withdrawal rate on the official inflation rate.
Sorry, I know that's pretty divergent from the thread topic but I do think the answer to inflation in investments is pretty simple, whereas people should be more worried about in respect of their expenses and how they can stick within whatever SWR they've selected if they hope to hope not to outlive their money. My expenses 20 years ago bear little resemblance to what they are now, so hoping I can just use my expenses today for the next 40-50 years, and just grow it by inflation each year seems like a fools' errand and not a topic I often see discussed in the blogs or forums.