did the wood that you burnt on your bonfire have paint on it? if it did i wouldnt use it, but thats my opinion, i would prefer not to put chemicals on my veggies and i would've thought that burning the paint would still leave a chemical residue.
if it hasnt any paint or preservatives on it then i wood (get it! lol) mix it in with compost for anywhere, but then i dont know which plants wood (lol) benefit best from it, i just think they all wood! (lol again! sorry :-[)