Personally, my wife and I have been investing for about 15 years together, and we've put almost everything 100% into stock mutual funds, primarily broad market indexes like the S&P500 and Total Stock Market style funds, for many, many years. There are minor exceptions--she had a retirement account from a previous employer that was evenly split among a bunch of asset classes, and we dabbled with a few individual stocks for a little while, we included some international funds, but mostly it was all broad stock market indexes. The theory really was we have a really long time horizon for investing, so it makes sense to take equity risk for equity returns.
A few years ago I read a book about asset allocation written for financial advisors, rather skeptically at first because I thought all this modern portfolio theory stuff looked overly complicated and must be for people afraid of stock market risk. It opened our eyes to why including other asset classes make sense. Since then we have moved a sizeable chunk into a REIT fund, and moved more into international funds (again broad indexes). We conceptually started with the book's argument for even weightings for different asset classes, but it also showed how most of the benefit of other asset classes came with even small percentages allocated to those other asset classes. Based on that we've taken it more gradually--right now there is about 10% in REIT and 10% in International funds, or 20% in each if you don't count the elephant in the room (read on). The rest of the mutual fund money is in S&P / total stock market funds.
Then there's the elephant in the room. We also have shares in a private startup company that may go public someday--the theoretical valuation of those shares (based on the last fundraising round) is about half of our portfolio. This causes us to want to skew towards larger companies elsewhere, which one could argue the S&P and market cap weighted indexes are, so we haven't added any small cap / micro cap exposure. It also causes us to really want to sell those shares, because we certainly understand the huge risk it represents, but we don't have any easy way to get out until they go public--I have reached out a couple of times to try, nothing actionable yet. It will be a very happy day if that comes to pass, but if it amounts to nothing we'll be OK. Overall we're not panicked about it, and don't want to sell at a lowball price, but if we could exit and diversify more, it would be a Very Good Thing.
We may be interested in owning real estate at some point, but at present we have no significant spare capital to purchase any--almost all of our investments are in retirement, college savings for the kids, and HSA accounts. Another factor is that my job is pretty high income and typically 50-60 hours a week and a lot of travel, so passive investments are a much better choice right now than signing up for the potential of calls about a leaking toilet on a Tuesday night. That might change when FI has been achieved.
I know a lot of folks on here are into dividend stock investing--I'll just say we've never pursued that, and during an accumulation phase have looked at dividend income as a bad thing vs. price appreciation, since it would potentially mean higher taxes compared to eventual capital gains. Since our income is high, our marginal tax rate is also high, so the math on that might be different for you.