Recent discovery for me - it might be old hat for you - is what useful masks you get by cutting the fingers and thumb off a disposable glove - perfect for covering up the head and arms of a figure
Here's one, though a little outside airbrushing figures, perhaps: I use old mail envelopes to mask sections of my airplane models, especially the wings. I hit upon that, after applying piece after piece after piece of masking to a surface.
I find plumbers tape works well as a mask too. That's the tape that goes over the screw thread on tap fittings to make a more water tight fit.
It doesn't stick to any surface and yet sticks enough to be a useful mask.