I've narrowed down the list of possible candidates and the logical conclusion is that it will have to be some kind of thin wall plastic with a tupperware style top.

There's got to be some food item in the grocery store that comes in a container like that and is small enough. It will probably be in the refrigerated section and it will probably be something that is wet or semi-wet and thus needs a tupperware style top. It will also probably be some food item that is expensive and thus comes in a small container. I just haven't found it yet.

Perhaps that description will ring a bell with somebody. I'm going to the grocery store this weekend to snoop around. I wish we had a better selection of stores around here.