I have wondered for years if the Apollo moon missions, especially Apollo 11, had any contingency plans in case they met either aliens or other humans (presumably Russians) on the Moon.
Granted that the Moon was well-known to be a dead world and finding native "moon people" there was extremely unlikely, who's to say if beings from some other world might be there for some reason or another?
It was considerably more likely that they might have encountered other humans. The Soviets, for instance, had actually planned to launch their own first moon landing just days before Apollo 11 launched but their mission got scrubbed due to technical issues and never got rescheduled. But NASA presumably knew about that mission and may have made contingency plans - which the Apollo 11 crew might have rehearsed - since the abort of the Soviet mission didn't happen until very shortly before Apollo 11 set off. Of course, the contingency plan was probably only needed if the Soviets had landed within walking distance of Apollo 11. I have no idea where they planned to land but it seems improbable that they would land that close.