Magento is officially not PHP 7 ready at the time of my reply to you. But there are a couple of fixes available for you to do for your site in order to make it work. Inchoo have developed something here which is for M CE 188.8.131.52 - 184.108.40.206. and reported working on M EE 220.127.116.11.
However the modules will still create some issues I believe.
Here is the link for you to try.
Please use it at your own risk after proper testing. I would recommend to wait a bit longer, little more than official release, by the time the module developers will also make changes to their assets for the big change.
Hope this helps!