I now buy Tempest aircraft plugs, fired by Magneto. I use auto plugs with the Pmag, they are Autolite 386 for the O-290, & NGK BR9ES for the O-360.
In a pinch, I don't mind mixing Champion, Autolite, Tempest, Auburn or other FAA approved spark plugs as long as they match the heat range of the others, and run well (EGT & CHT).
I also use Philips XC 20/50 oil, but don't mind adding a quart of Aeroshell or Exxon Elite if that's what is available at the FBO when traveling.