The mighty dragon roared ominously - there was little the warrior of the group could do but distract its fury whilst the mage stood back atop an outcrop of rock, his voice echoing words of arcane power - the only spell he knew which had a chance of halting this beast. As the spell was beginning to come into completion - a jade glow forming at the tips of his fingers - The mage cringed slightly in pain. Blinking, he tried to hold back the growing ache in his stomach but to no avail. Mere syllables from the end of his word he doubles over in agony, collapsing on the rock and clutching his stomach as he watches the dragon swipe at the warrior, tearing him in two...
Now, I don't really play table-top RP much, so I'm not too sure if this is something implemented often, but realistically it would be expected. In days without modern hygeine standards, preservatives and refined foods, one would expect a lot of rotten meat and bacteria-ridden fish to be eaten. It is quite difficult to believe that our heroes would never catch a dose of food poisoning and find themselves with insanely painful stomach cramps, or perhaps having to flee behind a bush to 'evacuate themselves' every 10 minutes. Anyone who has suffered food poisoning will know that it always seems to come on at the most inconvenient of times
and as such, perhaps if in your scenario the warrior fishes up a tasty treat from a nearby river, two days later all those who ate that fish will find themselves with food poisoning which may last several days. Every action they perform will require a saving roll of some kind, or they'll double over in pain and lose their turn.
More on that subject - animals which are poisonous to eat.
Would anyone in your party know that pufferfish are extremely toxic to eat? That many species of turtle can contain what is known as Chelenotoxin? That eating the liver of a seal can cause an overdose in vitamin A, which if taken too much of can act very much like arsenic? And lets not even MENTION all the varieties of plant which are poisonous! The world is a dangerous place, especially if you're hungry.