[Tom Goldman]

With a data recorder you need to look at what is necessary for performance and what is nice to have for peace of mind .
Voltage, tach and G-meters are standard with the RacePak Sportsman .
Oil pressure ,water temp fall into the peace of mind category, nice to have but not a tuning aid .
Fuel pressure and Vacuum fall somewhere in between , both can show performance related symptoms .
A 8 magnet driveshaft collar & pickup is in the necessary category to determine tire slippage on the line and down track.
O2 sensors are invaluable in determining tuning changes due to weather and for confirming results from changes . ... at least one channel is necessary ,preferably two.
EGT is nice to have as well if you're on alcohol .