A table to use when quickly generating a party of new characters that need to be plausibly together, in a scenario that has no other exposition-y backstory. Have each party member roll on the table once, with them as X and the player to their right as Y. This should provide a plausible chain of acquaintance for the group.
Alternately, if there is one or several characters who are already integrated into the setting/adventure, or who are more central to the plot, simply have every other character roll once for that central character.
How does [X] know [Y]?
01: They are family (by marriage or adoption if necessary)
02: Friends from childhood (happy)
03: Friends from childhood (tragic)
04: X formerly hired Y for some job (can be this job)
05: Former rival (if different class/skills, then rivals in some secondary manner)
06: X owes Y for saving X's life
07: Both met when hired by a third party for a previous job
08: X and Y were shown one another in a dream vision
09: Both were attacked by bandits en route to...
10: Met at a tavern, both drunk as hell
11: X moved in and lived as Y's neighbor for years
12: X was hired to kill Y, but changed their mind
13: Friend of a friend, met at common friend's funeral
14: X's mentor/parent commanded they accompany/protect/learn from Y
15: Former or current love interest (secret or otherwise)
16: Met in prison
17: Both (accidentally?) angered some powerful entity which they're both on the run from
18: Long adventuring buddies (all other party members dead)
19: X is inexplicably drawn to Y
20: Roll Twice.
