The massive bonfire you talked about Waggi, it seems they burned all kinds of stuff. What about heavy metals and possibly dioxin in the ashes. I don't know if these things can end up in your veggies. Dioxin is created when plastics are burned.
I'm sure some people on this board know about chemistry and I hope they will post more precise info about possible hazards when the ashes are mixed with soil where your veggies will be grown.