I use old contact lens cases. "Advances" (i.e., cost-cutting) in plastics have made these very lightweight, and with a free case packaged with some packaging. They're definitely water-proof, can hold all sorts of gooey products (I use them for neo sporin and lanacane), can be labeled with a sharpie (recommended), and are readily available. Don't need two containers? Just cut them in half and sand the cut line smooth.
BTW, I use old squeeze tubes to repackage sunblock. Not sure what my current one weighs, but I'll go out on a limb and suggest "next to nothing." The best source of these is bathroom garbage can of any woman into cosmetics :-).