Thanks for the additional details, Zomarzi; that really helped! Sorry you had damage, but very glad it was relatively minimal,
I've been thinking about the problem of what to do with the plastic sack. While its weight can't be reduced, if the bulk could be reshaped, that would at least help with the carry.
Looking at how small my sleeping bag and my silk liner each stuff, I wonder if a small compression stuff sack might make it possible to get the plastic bag down to the size of a soda can. If so, it could be stowed in a bottle cage or outside pannier pocket. In fact, it might even be cached for one's return. Until recently, I ran a "trap-line" of 25 geocaches, and I'm wondering if one could stow a stuff-compressed plastic bike bag similarly. You spoke the very thought in the back of my mind wrt it being mistaken for an IED, but if it could be tucked inside a roadside guardrail or perhaps a roadside culvert or drain, it would be wonderful to leave it there, just awaiting one's return. Being plastic, it isn't like it would be ruined if it became wet. Let's see...it could be submerged or even buried, and certainly disguised as something else.
Hmm. There's some real possibilities there, and I'll give it some more thought!
Being careful to mind the "cache in, trash out" philosophy, I still managed to make one cache that consisted of a beverage container appropriate to the setting where it was placed. I used a side-cut can opener to free the lid, and it was a tight-enough fit for friction to retain it on refitting. Perhaps in the right setting, something similar could be made to work while traveling, yet not present an unwitting threat to others' security nor draw the attention of trash collectors of any variety.
You've set me to thinking!
Best,
Dan.