I can't see how burning basically natural items can be considered any worse than taking them home and throwing them in a landfill. Burning trash paper for example can't be any worse than burning wood. (I am not saying hand warmers fall into the "natural items" category as I really have no idea.) I am assuming of course that no one was talking about burning the plastic wrappers.
Often it seems that the LNT mantra gets applied to the impact on the wilderness without much concern for the total impact on the environment.