I'm not really trying to spread panic here but I'm just saying, you should be in full control of your private keys otherwise you will lose everything.
Bitcoin is going to activate a soft fork (BIP148 - UASF) and that could cause a chain split. In order to be safe (on 1st August) :
Use a wallet that support UASF and give you control over your private keys. (Exchanges like Coinbase, Kraken, etc... are not an option) use Mycelium/Bitcoin Core/Electrum instead.
Try to not send/receive anything from 31 July 2017 until the storm is finished.
UASF (BIP148) is a Bitcoin Soft fork. A soft fork is a change to the software protocol where only previously valid blocks/transactions are made invalid.
Usually, soft forks need the miners (a certain percentage) to support them in order to get activated. that's not the case for UASF, UASF will get activated no matter one on 1st August. If some services (exchanges etc.) decide to not move with UASF, there will be a chain split (which means two BTC coins and two blockchains). To assure that you are safe, Its better to be the one in control over your private keys keys.
Private keys are what allow you to spend funds from your address. Exchanges, gambling sites etc.. don't give you control over the private keys. If they decide to not support UASF, and most of people are with it, you will be basically screwed. To get out clean from this chaos, withdraw your funds to wallets that you actually have control over your private keys (Bitcoin core, Mycelium, Electrum etc).
I tried to explain as easy as possible, I know Its not that easy to understand.