What instruments were "standard" in WWI aircraft?
If you are asking about military aircraft there would often have been a compass, oil pressure gauge, a not very sensitive altimeter, a tachometer and some sort of airspeed indicator. Not sure about fuel gauges. I have also seen bank indicators. There was not the standards for instruments as in later days and some items were specific to individual aircraft types. Some of these guys could fly a sort of instrument flight but had not much in the way of navigation aids.