Personally, I only consider equity and debt instruments. Other than that you have commodities (oil, gold, digital/crypto assets...) but commodities are basically speculative assets (from an investor's perspective). They require the ability to predict future prices with accuracy, which I don't think I possess. And if you're unable to predict future prices, the optimal portfolio to hold is one consisting of a total-market equity fund and a money market fund, in whatever proportions you prefer. This is known as the two-fund theorem. If you're interested in learning about "passive" investing, I can recommend 2 youtube channels: Ben Felix and the plain bagel.
I'd prefer to hold cash in a savings account, but the rates are so low now it just doesn't make sense to hold a lot in cash. I don't feel that safe in the stock market either.