<VV> low octane gas accident

[mhicks130 at cox.net]

So tonight I put some gas in the clinker and I was in la-la land and accidently put in 87 instead of 93.  Yikes.  It only took 7 gallons so it's half good stuff still.  It didn't knock and ping on the way home but I'm a little concerned.  Should I be?  If it does start pinging is there anything I can or should do?  On the other hand, if it doesn't ping, I wonder if I can't just put the cheap stuff in all the time.  

thanks in advance.

mike