Subpart 1.  Prohibition.  No person traveling over or using
state lands or waters within the BWCA shall have in possession any nonburnable food or beverage containers which are not designed and intended for reuse or which have little or no commodity value for reuse, including containers on which deposits are commonly charged by vendors.

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I don't know how staunchly enforced this is since many freeze-dried food packages use foil, as well as Pop-Tarts, Kool-Aid, etc. I have had my campsites and/or permits checked half a dozen times by park officials, with no complaints. I would guess that unless you leave behind a pile of foil wrappers, there will not be a problem.

Chuck