Along with the fabulous snack containers, I added one bag each of white and yellow unpopped kernels. And as luck would have it, I had recently been cleaning out a section in the garage and found a box full of fluffy white Styrofoam packing peanuts, which gave the excellent illusion of popped corn.
Now admittedly, L doesn't really understand what popcorn is or what it's all about, as her experience has been limited by my necessity to not let her choke. All the same, the sensory aspect made her lack of knowledge on the topic completely moot. The nice fluff of the packing peanuts complimented the hard little kernels, which made an excellent plinking sound in the plastic containers. L learned a new word, pronounced "pa-cone" and really stayed engaged in this tub for quite a while.
A word of wisdom from those with experience: if you are planning to do this activity outdoors, make sure it isn't a windy day. In the midst of all our fun, we spent a good deal of time chasing rogue packing peanuts all over the yard as they were carried away by the gusty wind. Other than that little snaffoo, I have to say we haven't had this much fun in while!