To hide some cash in a safe and put it where thieves wouldn't find doesn't take much.
Seriously. Even if it is obvious, you can secure it to the studs and floor to make it non-trivial to remove, and a small firesafe that you can hide is easy enough to obtain.
What is your fear of having your money in all index funds? just curious
Well, right now, I don't have much in index funds because I bought a house, and it turns out "I'm going to take a few months off work to work on the property and get an office built" means "No, you can't have a mortgage, you bum." Even if you can pay cash. With a signed employment contract.
In general, though, I suspect I'm a good bit more conservative with my investments than many here. I have the usual LendingClub and Betterment accounts (the second of which has been nicely losing money for me since I got it), but I also keep a good bit in various hedges - Bitcoin, metals, physical cash, etc. I'm interested in how to hold at least some value through substantial catastrophic events.
Why? I expect there's a decent chance that within my life (probably a good bit shorter), there will be an ongoing set of assorted "unrelated" shocks that mean index funds and the like aren't going to keep going up. At some point, we run into the limits of exponential growth on a finite planet, and I expect we're going to be hitting those sooner rather than later.
I've also been working towards "productive investment in my property." Gardens, greenhouses, solar, chickens, rainwater storage, etc. I see those as paying off regardless of which way things go - and, I'd add, I'll have some idea as to what's going into my body.
I'm aware this isn't a particularly popular approach around here, and that's fine. You make the decisions that make sense with your expectations of the future, I'll make those that make sense with mine.
I don't really expect to ever "retire" fully - I just expect to have the freedom to work on whatever I feel like instead of what other people tell me to do, and that tends to generate income for me.
If I'm doing what is standard on this forum and shoving a lot into the markets and the markets break catastrophically, I'm hosed. If I do what I'm looking at, I still have a good bit of stored value I can use, and can provide for my needs, the needs of my family, and to an extent the needs of my local community.
If the markets do what people here expect and keep going up? Well, then, I have a lot of income to play with and do interesting things with on my property. And I still eat well.