There are always enough seats on a Soyuz or a Space X Dragon for the current compliment but no spares. If NASA decide to the bring the Starliner crew home on a Dragon capsule the next crew (which is launching shortly) will be reduced to 2 from 4 to free up spare seats.
Consumables isn't an issue, there is always enough to account for at least one, perhaps two, failed re-supply missions.