Traveller: Companion - Rules of Play says:
The Traveller Companion is a compilation of variant and alternate rules. Variant Traveller creation systems allow specific tailoring, whilst alternate combat rules introduce hit locations and wound severity. Rules for hunger, thirst, temperature, atmospheric and water pressure effects make the universe more realistic, not to mention more hazardous. Encounters with animals and vehicles are also covered, along with the consequences of lawbreaking on personal and starship-operations scales.