I would suggest changing your fuel filter. The filters are very affordable, available at pretty much any auto store, and only take about 10 minutes to install.

This has always been the first step (in my experience) towards preventing or stopping engine ping. The car still might ping for about 50 - 100 miles after the filter change, but if it's going to stop, it'll stop very shortly thereafter.

I had occasional pinging not very long ago. Changed the fuel filter, and all was well.

BTW - I am in CA and the only high octane fuel available at the pump is 91. Only last week did I try adding octane booster. So, try the fuel filter.