What items will be considered valuable in a great economic depression? Here's what I think will be:
1. Food - Seeds, eggs, meat will be the most valuable
2. Purified Water - a human essential
3. Livestock
4. Ammo - Never bring a knife to a gun fight
5. Precious metals - Gold and silver will continue to be used as currency
Also it's why gasoline goes bad when stored for long periods.
I really think vacuum sealing a fully filled gas can would do the trick.