An inert sidewinder round has a seeker head so the pilot can hear the "growl" in his headset when the missile has acquired the target.
An inert AMRAAM could also be carried that has the electronic package of an AMRAAM so the aircraft systems think they are interfacing with a missile. That is necessary to conduct BVR missile engagement training.
There are also pods that look similar to inert sidewinders that are actually a form of datalink. On an instrumented range this provides aircraft data (including fuel state, weapon state, aircraft flight parameters, etc etc) to the range systems both to declare who has shot who during an engagement and to provide data for later playback during debriefing.