|Buying a can of seeds and tossing it in the closet|
does NOT make you prepared to grow food
post-TEOTWAWKI. That's silly.
Really? Think about the use scenario here. There's been a societal collapse so drastic that markets are shut down, and shut down for long enough that you can go from planting seeds through to food production (several months). You've got a can of seeds, which you need to plant, care for and then wait for them to produce. How well do you think that will go for you?
If you're a skilled farmer/gardner, that may be one thing...but if that describes you, you probably don't need a #10 can full of survival seeds. You already have a garden/farm going, which you may be able to keep up post-collapse. A can of seeds isn't going to be much help there (though you may want to use heirloom seeds now).
If you're a gardening/farming moron like most people I know (myself included), then you're not going to get much, if anything out of those seeds. You need fertile soil, water, sun, security, know-how and time to go from seeds to food producing plants. Most people fail miserably for the first few seasons they try their hand at growing, and that's in normal times, with all of the modern resources at hand. If you're blasted back to the stone age, starving and worrying for your life, do you think you'll fare much better?
So ya, I think these cans of survival seeds are generally pretty silly things, providing a false sense of security for many. If you want to grow your own food after a disaster, you need to start before the trouble hits. If you're going to grow-your-own, get a robust garden going now, learn the ropes and make the mistakes while the costs are low. Certainly don't chuck a can of seeds in the survival cave and think you're good to go! You'll be pretty disappointed when crunch time rolls around.