Also remember the Tupperware pieces used for the Sandtrooper backpacks. Look for pieces used in other parts of the movie that may have had other components not used for that prop that were available for re-use elsewhere. Also also, the Jell-ette molds don't have flared tops -- there's a slight outward angle to the upper portion, but it's straight all the way up, not counting the slightest lip for the lid to attach to. The lid, on the other hand, if one cut off the outer portion (that locks it onto the mold), looks like it'd drop right into the top of that thing, and may be the "flared" black lip people are seeing.
I've some speculations for the rest, but nothing to base it on beyond ways it could have been done, that I could do. *shrug* All with Tupperware.
