Simply put - nothing. Just wait hard fork, after that if you're keepin your bitcoins in exchange, they may or may not give you Bitcoins BIP148 and BCC. If you're keeping your bitcoins in private storage, then just wait until wallets will make official announcements what version of which wallet conforms with BCC code for sure. Right now it's a bit of commotion.
How does this compare to the ethereum fork a while back? Coinbase credited me with ETC for the ETH I was holding at the time, so I wound up with both. While the ETC initially was worth peanuts, its recent rise made it worth something. It was free money for nothing.
Am I correct in understanding that if I keep BTC at Coinbase, I'll get no BCC (since they said they won't support it)? And if I move the BTC to my own wallet (or potentially another exchange), I will get the BCC?
Somehow this seems wrong. Just by moving the BTC to my own wallet, I can get BCC as free money that may be potentially worth a great deal, as with ETC?