For me the most important equipment is the stuff that's relevant to the air war like the Chain Home radar system, and Rebecca/ Eureka transponder systems.
The British and Ameriancs were operating portable radio transponders equipped at the platoon level for airbourne infantry as well as armoured groups.
Spitfires, Typhoons, Tempests and others were able to tune to these frequencies and find the signal sources up to an accuracy of some 50 to 100 yards.
Things that make the air war more interesting.
And an excuse to actually *use* some of the systems that warbirds had apart from their guns.
Not everything was dogfighting as I'm sure we are aware.
Also horses are a fantastic suggestion.
edit:
The AN/UPN-1 radio beacons used by the USAAF in conjunction with the airbourne forces is also a very important piece of equipment in my opinion:
If airbourne infantry and the ground support thereof is to be simulated of course.