Since we now finally have access to a military jet - Indiafoxtecho's cool Aermacchi MB 339 - my first instinct was to buzz the ATC tower at my home town airport "Maverick-style", and then fly the Mach Loop (also called the Machynlleth Loop) in Wales. Officially this is the Low Flying Area 7 (LFA7), a military low flying training area for fighter and transport pilots.
It is located in an unrestricted and populated area in Snowdonia. If you ever get there, you may get lucky and sit on one of the mountains surrounding the valleys watching RAF Typhoons, Tornados, C130s, USAF F15s or Ospreys fly past below you. Or you just get buzzed by them driving in your car :-)
These two flight plans recreate the Mach Loop with waypoints from EGOV (RAF Valley) to either the South or the North entrance. My recommendation is the latter since this way you can fly the whole loop. Optimal speed IMHO is between 300 and 350kt.
I did NOT create these flight plans myself. They were originally created by Dave Symanow, so please respect his wishes. Please refer to the included readme file for further information. These flight plans were originally created for FSX, but work fine with FS2020.