I think the GPS is a good idea, as you never quite know what you will want to analyse later.
Noting the QNH, ground temperature (and ideally the OAT at some relevant height) allows for some CAS/TAS conversions later.
Which is important because at altitude your TAS should be higher and your turn rate (at any given bank angle) should be slower, though the angle of descent should be the same.
Which, if I have this right, means that real turn backs are harder on low density days, with the height loss inversely proportional to density.