If sentences like
I have something to eat.
are translated as
Mi havas ion por manĝi.
as it would be in French, then what about sentences like
I have something about which to think.
I have nothing onto which to jump.
That is to say, is the "por" still necessary here?
Mi havas ion, pri kio [por] pensi.
Mi havas nenion, sur kion [por] salti.