I want to hate your comment so much but reality is reality.
Plastics just don't really get recycled. Despite the efforts made (the company I work for included), recycling is such a joke because it's hard to even FIND sources that WILL recycle certain things because at the end of the day it likely doesn't exist because it's more expensive and sometimes has an even greater impact on the environment to recycle than to just keep buggering on.
That said, I don't like you burning plastics. I grew up burning paper trash in barrels but we were still mindful of not releasing toxic fumes into the local environment. So, fuck you for that one.
I don't know if it would work with a Big Mac but I'm curious to know. I imagine the lettuce would have to mold, but McDonald's shreds their lettuce so maybe it would have time to dry out ¯(ツ)_/¯
I know it's been done with a McDonald's burger and fries before though, and I think it looked the same after a decade or more.