Is the party just the PCs or do they hire a torchbearer with more GP than he makes in a year? Maybe a mercenary or two promised a half share they will never live to receive. Maybe a spear carrier here and there. I doubt [m]any parties would take this to the Zapp Brannigan level of sending wave after wave of NPCs at the monsters until they reached their stomach limit. But if they did, do tell.
Hireling, henchmen, extras and redshirts.
In previous editions, it seemed common enough that the players brought hirelings, pack animals, torch bearers and other types of extras with them. Some might not go into “the dungeon”, but having NPCs with had some uses. Hackmaster, in a bit of gallows humor even expects the players to have these red shirts with so that when a deadly monster shows up, the players can see they are in over their heads by how fast the NPCs get cleaved trough.