I've included my specific platform below, but this question should be applicable to other platforms just as well.
Board:
Matek F411
Platform:
BetaFPV Beta65 Pro 1S (65mm m2m)
I know there are serial logging devices specifically to provide BlackBox for boards without onboard flash, but my concern is that given the very narrow power envelope of these micros that any data collected with an external logging solution would be scaled improperly once the micro is flown without the logger onboard.
OpenLager is one solution. Tuning with auditory inputs is another (it's usually possible to hear oscillations caused by excessive P or D gains), but this is more challenging. This is made significantly more challenging because often props are poorly balanced, and this can imitate the same sorts of errors.
Unfortunately, trial & error tends to be the best answer to this. As far as general trends, in the sliders most often stock master gains, 0.8-0.9 P/D Ratio, and slightly high P&D Gains (1.1-1.2) will work well on quads with good motor authority (1202.5, 1103 >10,000KV for 1S quads). Thrust_linear = 50 is also something that produces pretty great results. The harder one is trial & error on filters - quite often you can work iteratively towards the right with the gyro all the way out to 2.0, and the D term filtering will end up somewhere in the 1.4-1.8 range with these PID settings.
