"If I see one more garden vegetable, I'm going to kill myself."
Here's a way of updating the food system to add a little more depth - Food could have a gradually increasing happiness penalty whenever you eat the same thing too often over a period of time. Once you get a nice farm set up, it's fairly easy to live off of cabbage and potato soup indefinitely, but would you really want to? By the third bowl, you'd be tired of it, and after a couple days you'd kill for anything to make your meals a little more interesting.
Food could be tracked by individual items as well as broad categories (meat, vegetables, fruit, fish, processed food, etc.) Cooking your food in different ways could help to reduce (but not eliminate) the penalty. There could be a pair of opposing traits dealing with this as well. A gourmet would become unhappy very quickly with repetitive meals. A simple eater would have no problem with a very plain diet.
This could add depth and strategic choices to the game. Right now, if you catch something with fishing or trapping, it's just a little bit of extra food to add to your diet. But realistically, you'd also be ecstatic that you could try something new to break up the monotony of garden salads. This would add an incentive to invest in more food sources. I don't plant radishes, carrots, or strawberries because of the complications of overwatering/disease, but I might if there were some extra benefit to doing so. You'll also need to decide what to do with all of your canned food. Right now, you simply let it sit on the shelf unless you have an emergency where your fresh food runs out. But instead, you'll be tempted to use some of it occasionally. Do you sneak an occasional can of tuna and a brick of ramen noodles into your diet, or do you save them for the winter?
The only issue I see with this is that since it depends a lot on unhappiness, it also depends on that mechanic eventually getting a bit more fleshed out. Right now depression isn't that much of a threat. This would at least go some of the way towards improving that system. Currently the only time that sadness really causes a problem is when you're staying inside for too long reading skill books or eating old food. But I can get huge bonuses to happiness just by tossing the same ingredients into a stir fry every day when realistically, that would be one of the more depressing things about the apocalypse (besides everyone being dead.)
