The problem with using cards for it is the same reason the Tyranid psychic power cards are useless. You have them en mass, so you can't just keep the cards on the unit or in one place as there's a fairly high chance of multiple units rolling the same thing.
For example, your typical Tyranid army has at least four psykers (counting any size brood of Zoanthropes as one psyker), usually a Hive Tyrant or two, a couple of broods of Zoanthropes and maybe a Tervigon. When you're rolling for that many powers you're probably going to get some doubles, so unless you buy multiple packs the cards are useless, you're better off just keeping a little pad and pen with your dice and templates like I do.
The same goes for combat drugs, if you had them per unit you would likely get doubles, and if they stayed as they were you wouldn't need cards because you would only have to remember one roll anyway, and they aren't exactly a lot to remember like some psychic powers, they're very simple things like +1 to a certain stat or re-rolls.
"Oh how awful, did he at least die painlessly? To shreds you say? Well, how's his Dracon holding up? To shreds you say? Very well then... Sad, sad, terrible gruesome news about my colleague Archon Mhu'bhutu." - 'The Feather', Dracon of the Bladed Lotus