If you can't trust your executor with your passwords while you're still alive, how do you trust them with your estate after you're dead?

Safe deposit boxes are good places to put sensitive stuff that you want to keep private until after you're dead. Put a paper sheet in there with your passwords if you're worried about it.
Just don't forget to document which bank you maintain the box at.

Best thing you can do is make an appointment with an estate lawyer. Most likely they will recommend you set up a trust and move the vast majority of your assets to that trust. Then you can set up co-trustees (who you want to have access now) and/or successor trustees (who gain access after your death).

Things like insurance policies should have your spouse (or whoever) as the beneficiary, and then the trust as a secondary beneficiary. Rental properties should be owned by an LLC, and then the LLC is owned by the trust. Bank accounts should be in the name of the trust.

An estate lawyer is not free. But they're worth it to set up a good estate plan (which if done right, can most likely keep things totally out of probate - depends on your state though).

Online access to accounts is probably not as important as you think it is. Generally, your executor can gain access by supplying a death certificate and documents that specify him/her as executor (usually specified in your will). It is important to have these accounts documented for your executor, but online access details are not as important. Often times when someone dies access to their stuff will be locked down as soon as the powers-that-be find out about the death. Being a co-signer on a bank account won't help one bit when the account is frozen due to the death. A trust-owned account with co or successor trustees is better. Another reasonable plan is to move money that is immediately needed out of their account before they die, or second best, before the bank freezes the account. Move quick. The executor will eventually gain access to the frozen accounts, but that takes a while and funeral homes want to be paid immediately.

As far as finding stuff after you're gone, good luck! It's a nightmare for anyone trying to do that. My plan is to keep "the good stuff" more or less gathered together for family, leaving the crap stuff to be spread over the rest of the house. Then have your executor advertise a free-for-all for the masses. Grab-and-go without looking at what you're grabbing is $1 an armload. Taking more than a minute to grab a bundle costs $10 an armload. Purposely digging around to find the good stuff is $50 an armload, decreasing to $25 an armload as the house is mostly cleared of junk. If you try to too tightly manage your junk dispersal - most of which nobody but you wants anyway - will end up with your executor having a house full of junk they can't get rid of, praying for a fire to sweep through and burn the the place to the ground.