Back to the poison, I like the ration idea. You could use the poison as an attack, and a trickery weapon. For example, you are with a group of players that are trying to figure out a plan to get off the island but, it seems hopeless and you have poison, just sneak in the poison and you would be the winner, it would make an edge of paranoia to always be around. Also you shouldn't just have poison for on time use, that takes the fun out of it, make 10 or something.
One more thing, I think some randomly placed weapons would rock. I am not talking about any M-60, but I think a poll or something like that... especially if you have poison and want to act like you got another weapon to backstab your friends later on.