Here is what I would love to see in card form to make things easier (though I don't know how realistic it is):
Summons: Instead of having to pull out the bestiary, and write out a stat block on a notecard or something every time a monster is summoned, you can just hand them the card for the summon (or the whole deck beforehand and let them find it), and everything they need will be right there!
Spells: A number of cards with the rules for each of the spells on them so that they can be kept with spellcasters so that they will have easy and quick access to them.
Both of these would be a bit tricky, as there are a number of each (especially spells), and they would likely have to be split into separate decks, but they could be very handy. I especially want a deck of summons, because it almost always causes the games to come to a halt any time one of those is cast. We have a token set for summons, why not cards?