Jaster Mereel didn't had one on his last battle - aswell as the Company of True Mandalorians he was leading. + Young Jango leading his Company of Ground-troopers aswell.
The Deathwatch Guy's liek Tor Vizsla also.
Some Deathwatch Guys in the Clone Wars dont have a Jetpack when they steering a Speeder - makes sense ^^
Mand'alor the Ultimate and his Predecessors are not known for using a Jetpack. The regular Neo-Crusaders in the mandalorian Wars didn't sport Jetpacks in general. Only the Veterans and Elite-Troops carried them, not the fresh Grunts. The Retro-Crusaders in SWTOR sometimes have jetpack, sometimes not ^^
Alot of the Book Charackters like Kal Skirata or Walon Vao know about the risks of Jetpacks either.