In reply to above:
Packaging long gone and no clues on the shrivelled remains (the handwarmer's - not mine... yet!) of a manufacturer.
I saw that particular Wikipedia page which is why I'm not too concerned if it was sodium acetate.
The wiki page for handwarmers says they "typically" contain sodium acetate but I can't find reference to anything else they may contain. I suppose if it was anything particularly toxic I wouldn't be posting here!
Still, I wonder what else it could have been?