What happens to our investments, SGX, CPF, insurance, banks, etc in wartime?

Commodities would be king in wartime. Buy Gold and hold till it's safe to go out again.

War in backyard?

Depends on whether the banks, sgx, data centers, factories, offices etc survive the bombing. If they do, there is a rare chance you may see your investments again. Though of course, likelihood is that the "local companies" do not survive well - imagine half or more of the employees dead or the factories bombed.

I think it's better to count one's blessings that he is still alive (or sometimes better dead).

At that point, it's likely everyone starts anew... and is more concerned about basic survival and maybe bartering for limited resources.

Just look at the other wars for inspiration?

Safe place to park is where there is no war. E.g. other countries. Or if you are talking about gold or silver.. find a good place to bury it and make sure it's not stolen by thieves. It will come in handy if you survive.

If am not wrong, your insurance is excluded from payouts in time of war. But you may still be covered when war ends, if the insurance companies are based overseas and survive? Or come back after the country restructures? Then again, it's either they honour it (based on what's in their system) or you can find your policy documents... Maybe. Just maybe. I don't know.