When you gain skill points or a feat, do you have to spend
the points or choose the feat right away? Is there any way
to save skill points or feats?
You have to spend skill points or choose feats as soon as you
get them.
There's no reason for DMs to be absolute about this. If
you're running a campaign and one of your players just can't
decide right away, it's okay to let the player wait awhile, but
the character must spend the points or choose the feat before
the character in question gains another level. Just delay all the
benefits for the new level until the player spends the points or
chooses the feat.