It should last a good while - depending on the bag and seal.
I like to keep a 6 month stock of tobacco in advance even now - I’ve smoked bagged tobacco that was bought a year before and it was fine. I have tinned pre-SCHIP cig tobacco from ‘09 that’s still good.
5lbs straight may be an issue if/when the SHTF as you’ll need to deal with it then when you crack open the bag. I’d stick to 1/2 and 1lb bags/portions for long storage and use when needed for trade or smoking.
When all else fails you can always rehydrate the tobacco - keep a write up of how to do that with the tobacco, but I would rotate stock anyways and use that up now - the trick is keeping it fresh - 5 lbs is over 12 cartons worth-that will take a long time.
Break it down into manageable quantities - say, half a pound - and then seal it in those heavy plastic food bags with the little plastic sliders.
Then fold the top over two or three times and tape over the whole top/slider area with heavy duty duct tape.
I’ve kept tobacco for one to two years that way, and it stays moist.
I have used a damp paper towel, place in the bottom of one of those vacuum sealed bags, add the leaf. Oxygen is also your enemy so drop in an oxy absorber. Then vacuum seal the bag. Keeps a really long time.
Store bought cigarettes are a very refined product, a well preserved pack in a post collapse world would be very elegant and prestigious indeed, high quality bargaining.
I had a few packs of luckys that were at least 20 years old and may have been much older ( I think they were much older) and at 2:00am when they had had a few drinks and were out of smokes, not a single guest ever commented on them as old or stale, a couple of people when prodded could detect that they seemed a little less than fresh but they had no complaints.
Thanks to all the FReepers for their recommendations!
What I did was this:
I have a bunch of large, sealable plastic bags that smaller quantities of the tobacco come in. So I took four of those, put about 12 ozs. in each, then took the four and put them (sealed, of course) back into the large plastic bag the original came in. But before I sealed it, I took a paper towel, wet it and smushed it up, wrapped it in aluminum foil, and put it in the bag.
The remaining amount was enough to fill a 1 1/2 gallon plastic jug, so it went in there with it’s own towel/foil thingie.
I will check it on occasion just to make sure it’s not getting moldy or whatever, but I very, very much doubt there is enough water in there to make it damp. Just enough to keep it from drying out and getting brittle.
Smoke em if you got em!!