Are you thinking in terms of days, weeks, months? If you're talking about the typical canoe trip, I cut the HBB into squares and put them in quart-size ziplock bags. I've then taken them on a week-long canoe trip and had a couple uneaten bars left at the end of the trip. I ate them a week after we got back and they were perfect.
How long would they last in a airtight container? I'm not sure, but I'm sure they would last at least a few weeks. Just a guess...
"Keep close to Nature's heart, yourself; and break clear away, once in a while, and climb a mountain or spend a week in the woods. Wash your spirit clean." ~ John Muir
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