Pick a color and make these the PC cards. Include on them things that you don't want to have to ask the players at crucial moments. I recommend AC (regular, touch and flat-footed), Saves and any skills that you might want to roll secretly but at least Spot, Listen, Search, Hide and Move Silently.
Pick another color and make these cards to keep track of Magic Items on. You can write them up beforehand if the PC's have easy access to identification magics and you don't want the bookeeping. But for low-mid level games I would write something like "Longsword #14" at the top of the card. Beneath that give a physical description of the item. In your notes you have a magic item list and next to #14 it says "Wizard's Weal: +1 Sword of Spell Storing". As the players get the qualities of the sword identified then you give them the information from your notes to write on the card.
Pick another color that is common (White is probably best) and use these to write down stats of adversaries. The format I use is:
<Name - Race - Class/Level> <Hit Points>
<AC (Touch) (Flat Footed)> <Armor Worn>
<Attack Bonus with primary attack> <Type of weapon or attack> <Damage>
<Attack Bonus with secondary attack> <Type> <Damage>
<Attack Bonus with tertiary attack or ranged attack> <Type> <Damage>
<Fort Save> <Reflex Save> <Will Save> <Magic Resistance>
<Important Skill Bonuses>
<0 Level Spells>
<1st Level Spells>
<2nd Level Spells>
<Etc...>
<Magic Items and other treasure>
When combat breaks out I place the PC's stat cards in order with the adversary cards based on initiative and then just flip each one to the back of the pile as their turn is over.
I don't know what you should do with your other cards but I'm sure there will be other good suggestions in this thread.
