So if I have coin on, say, coinbase, what should I do? Should I withdraw it to a wallet before August 1, so I can access both Bitcoin and Bitcoin Cash?
But don't trust any third party with your coins, especially Coinbase which isn't sharing the private keys with you.
Take your money out of an exchange, it should not be kept there in the first place! If you don't own the private keys, you don't own your bitcoin. If it is on coinbase, you don't control it, you are just asking them for permission.
So I'd have to figure out a wallet strategy that made sense. Maybe I'll make a paper wallet this weekend? Hrm, security is hard.