LOL My comment was more of a joke about people who always jump in to say something like, "we did that decades ago..." fill in the blank, myself included some times. ;-) Anyway, the "invention here I jokingly refer to IS the trash bad as pack cover.
Anyway, the use of a garbage bag for a pack cover, ground sheet, emergency VB "jacket (one saved me one time), seat, foot warmer, tent patch, pack liner, rain skirt, impromptu sleeping bag component, rain jacket and on and on, is as old a garbage bags themselves. I always carry one or two in my emergency kit, and I would guess a good fraction of the people on here do as well. Weirdly, seema like I used them a ton, in spite of the fact that in "Marko Style" they are supposed to be back up stuff. I need to think about that more!
It is usually best not to do the modification until the need arises IMHO though - then you keep the customizability, and will have more options later on. For instance, you garbage bag vest/rain jacket will tend to work better if you don't have to mod it out of a bag already ripped to be a pack cover, and so on. However combine a few garbage bag with duct tape and you can re-purpose I suppose.
I'd like to see you make a denser video collecting and demoing a bunch of different backpacking uses you could get out of a humble garbage bag - especially if you can come up with a few that aren't common knowledge. Even the process of collecting the oldies but goodies all in one places would have a great value.
"Here's one of my many critter style bag unpacks from a trip that was unheard of and considered impossible"
EDIT: I watched your video, and thanks for making it. I like the fact that you don't mess around. There are a lot of such videos that, style-wise, have way too much air, or comments that are just incidental. I also love your backdrops, from the mountains to the "still life with napping dogs". Those are excellent - keep those up. Don't want to see some guy's kitchen when the topic is backpacking. I too agree about using cheap stuff if possible.
As for cheap - I like Mike Clelland's recent book - as simple and paired down as it is, it comes closer to anything I have ever seen to the spirit of ultralight backpacking, including on here, in the past 15 years. Both in form and content. And he always emphasizes the use cheap stuff when possible. On the other hand (Ryan Jordan and many other have written about this starting years ago), there is an equally relevant issue about disposable gear you should consider as well, at least long term.
But I get you are coming at the problem from a particular view, and with a particular set of goals in mind. Go for it! There is one particular issue that you may eventually need to address, as I see it, whether motivated by UL backpacking, survivalist, or bush craft values. That is this, if you are ever using these method (especially the sleeping in debris piles) for longer periods you will have to address more "what if" issues. Do minimalist backpacking for a day or two, especially if you are always a days walk from the road is one thing. What do you carry if you have to be utterly self sufficient in any possible scenario. I don't think debris pile are going to work, or available in the right type and quantities to keep you alive in certain conditions. Just something to keep thoughtfully considering as you go forward.
You don't want to die just because your mylar space blanket ripped or otherwise became unusable the second night out, and it will at some point. Have a backup if you can even imagine a scenario where a lifesaving necessity goes caput.
However, not sure what you mean by "was unheard of and considered impossible". Don't think your kit in the video qualifies in either of those categories, and least not here. Or did you mean the trip/route itself. if the latter then THA is you lead - don't bury it.
If you drop a post here in the gear list section I'm guessing you could get a lot of advice from people here that would help you go lighter AND cheaper, if that is your goal. Good luck.