Never sub for an unfamiliar second grade class when you don't feel well, or have a canker sore on your tongue, or both. On a happier note, elementary students have their plusses:
They actually like you! (usually)
And oh the pictures!
I have also received as gifts, a half eaten fortune cookie, a broken frog eraser top, and several origami frogs of all different sizes (these kids were obsessed with frogs).