They will last longer, but they won't last indefinitely if they have fats in them--which most milk chocolate and nuts do.
You can store cocoa indefinitely in mylar w/ O2 absorbers, but it's the fats that are the main issue.
How long would they last in mylar w/ O2 absorbers? I speculate 2-4 years. Snickers is unfortunately pretty fat-laden (130 calories from fat out of 280 total in their 2-ounce bar), so it's hard to imagine you'd go beyond a couple years. If you google shelf life and snickers or other candy bars, you find shelf lives in the 12-month range. Now, I've eaten candy bars that have been around for a while, and never had an issue with them--things like Halloween candy--so I suspect that's conservative. But beyond a few years in mylar, I doubt it.
FWIW: Why not just get as many as you'd like to store, and rotate as you eat them?
Here's a repost of a post I did a few days ago regarding Hershey's chocolate syrup. It has a long shelf life but there are no real fats in it. Same w/ Cocoa. I've looked at milk chocolate and other chocolate products, and if they have fat, it's a signal of short shelf life:
Googled shelf life of Hershey's Chocolate Syrup, ended up at this site:
http://www.thehersheycompany.com/con...ore-chocolate?
Where it says, among other things (and it's worth browsing the FAQ about storage):
Q. How should I store chocolate?
A. Solid chocolate products will maintain their quality if well wrapped and stored in a cool, dry place (55-60°F). While refrigerated chocolate is certainly safe to use, we don't recommend it. Chocolate kept in the refrigerator may "sweat" when brought to room temperature and may not melt properly.
Cocoa is considered a non-perishable item which should maintain quality if stored at room temperature in a tightly sealed container.
Now, that's not chocolate syrup, but if you examine the list of ingredients in chocolate syrup, there doesn't appear to be much there which has a short shelf life. It's mostly various sugars, cocoa, and some emulsifiers.
Here's the nutrition label for it:
http://www.thehersheycompany.com/bra...chocolate.aspx
There are no calories from fat, which is a good thing since fats are the worst when it comes to storage.
Here's a site that purports to go down the list of ingredients, and they match the ingredients of a generic brand of chocolate syrup we have here in my house:
http://simplydixon.com/2010/07/hersh...-is-it-really/
I think the StillTasty site is uber-conservative in the shelf lives listed there; I don't rely on it for authoritative information on shelf life.
As I read the above and more, I'm reasonably comfortable in saying that such syrup has a long, long shelf life, five years or more (this is me talking, and I'm just bits and bytes on the internet, so take my opinion with the grain of salt required).
BUT--on the Hershey site there is this:
Cocoa is considered a non-perishable item which should maintain quality if stored at room temperature in a tightly sealed container.
I'm going to lay in some chocolate syrup, *and* some cocoa. If there's a better comfort food, I don't know it. Well, beer maybe.