First of all you'll need all the required instruments under FAR 91.205 (d). Per the PTS, you're required to do both a precision approach (ILS) and two non-precision approaches (VOR, LOC, GPS, etc.). I would suggest at least two NAV radios with separate CDI's, although one is only required but would create more work (like Rickair7777 said). Other than that ADF, DME, and GPS would be "nice to have" things but not necessarily needed. Hope this helps!