The following sentences will be wrong if “s” is omitted from those words:
If you play your cards (not, card) well, you may triumph.
One’s children are one’s families (not, family).
The refugee was seen with his effects (not, effect. Effects means baggage).
Having won the trophy three times, my club has the trophy for keeps (not, keep).
We do not know her whereabouts (not, whereabout).
GAB