This might sound redundant, but I would like to see squirrels running around conifer forests, they could act like rats and could be made into squirrel on a stick just the same way as rats.
We could also have new trees like pears, just use the apple tree as template and change it slighlty so that the red aples are now yellow.
Also, new insects would make the game more life-like, like grasshoppers, fireflies, beetles, butterflies...
Also, these insects could be spawned depending on the hour of the day, grasshoppers during the day, fireflies during the night and such.
I know implementing these would need some work on the grafics for each, but im sure some like the pears would be quite easy to make.