An Apollo Buddy Secondary Life Support System (BSLSS), consisting of: 2 water hoses, 8½ feet long and 3/8 inch inside diameter, to carry coolant flow between working PLSS and the other crew member; flow-dividing connector on one end of the double hose, being a PLSS water connector coupled with a receptacle to accept a PLSS water connector, blue-anodized aluminum; a 4½ foot restraint tether with hooks for attachment to the pressure garment assembly, i.e. at the astronaut's hips; a Beta cloth thermal sheath the length of the hoses, with locking tether clips 2 feet from each end; a Beta cloth thermal pouch for stowage of the assembly on the PLSS during EVA and in the LM cabin during non-EVA periods, 17 x 12 x 1½ inches. In final form, one end of the double hose would be fitted with a normal PLSS water connector.

RARE APOLLO BACKUP LIFE SUPPORT SYSTEM. Objectives for the Apollo missions 11, 12 and 13 required the astronauts to be no further than a half-hour's jog from the lunar module. In the event that one astronaut's Portable Life Support System (PLSS) "backpack" failed, the Oxygen Purge System (OPS) mounted on top of the failed PLSS could provide CO² purging and cooling for long enough to allow the astronauts to reach the LM.
Apollo 15 through 17 involved the lunar rover, and excursions much farther from the LM. In the event of a PLSS failure, the crew would have difficulty returning to the LM in time. Hence the Buddy Secondary Life Support System.
The BSLSS was a set of hoses and connectors which allowed the astronaut with the functioning PLSS to share cooling water with his partner; the stricken astronaut could then run his OPS in low-flow mode and run it for twice as long as in high-flow. It is a similar idea to divers sharing scuba equipment.
The BSLSS was first used on Apollo 14, where it was stashed in the Modularized Equipment Transporter (MET), the cart towed around the lunar surface. On Apollo 15 through 17, it hung off the back of the seats on the lunar rover. In use, it would strap onto the lower part of the PLSS.
Fortunately, none of the moonwalkers needed to use the BSLSS. As Jack Schmitt commented, "it rings a very vague bell that we had something called a Buddy SLSS, and the fact that neither of us remembers much about it shows how much we felt we'd need it!"