Thanks, Kris. Your posts always get me to thinking more about these things. 
Doesn't look like there is much to add or much further interest though? Here's an update with the TVS info I have. I tried to give proper credit for each item. If I picked the PTC part numbers I would probably get them wrong so any help with selecting the correct PTC part numbers would be much appreciated.
The updated list so far:
PTC resettable Fuse - 1.1A hold, ??? trip for ERR Cruise Commander Lite (GRJ)
PTC resettable Fuse - ??? hold, 250mA trip for passenger car LED lighting (GRJ)
PTC resettable Fuse - 0.5A hold, 1A trip for Fastrack Uncoupler tracks drawing about 1.8A (other brands may have similar requirements?) (PLCPROF)
TVS Conventional - Digi-Key Part Number 1.5KE36CALFCT-ND - 1.5KE36CA - 36 volt, bi-directional - Sized for a PWZW when the whistle button is depressed. This peaks over 33 volts if the compensation winding is considered. (Part number recommended by many, explanation by Dale H) (Digi-Key part numbers from GRJ)
TVS Command Control - Digi-Key Part Number 1.5KE33CALFCT-ND - 1.5KE33CA - 33 volt, bi-directional - Sized for the modern 18 volt bricks. The 18 volts peaks a bit over 25 volts. (HiRailers Unlimited & Independent HiRailers Group, explanation by Dale H) (Digi-Key part numbers derived from GRJ's above for 33 volt version)
For the TVS I believe the 1.5KE36CA is most recommended here on the forum and also the most widely used as it seems it would be suitable for either the modern bricks or the transformers with whistle buttons.
All corrections and/or additions welcome.
