Edible but not too tasty, but disposable and biodegradable at least...
I don't know why I didn't think of this before. Back in food science class, we scooped out the fruit from oranges, leaving the shells intact except for part lopped off the top. We juiced the fruit, added sugar, gelatin and cream, put this into the emptied orange shells, then chilled it.
If I cut a bit more off the top, it would make an excellent glass. In India we have sweet limes, which are as big as oranges, so I used the juice for a fresh lime soda:
1/4 cup sweet lime juice
1 1/2 tsp. sugar
a sprig of mint
4 ounces soda water
Mix all ingredients and pour into the emptied sweet lime shells. Garnish with a sprig of mint. In summer, freeze the fruit shells to stiffen them up and provide extra cooling. These can also be used for ice water or fruity cocktails. Of course, coconut sheels and hollowed out pineapples have long been used as beverage containers.
Next I try stiff, frozen gelatin cups...