I use pretty much plastic bags that are at least freezer bag size, or larger, that I'm able to zip up to store my dry leaves (I order the 8-12" ones, and the guy I get them from tends to send them in good storage bags). They are fine when stored in a dry spot for a long time - unsure exactly how long, but I know at least months.. just as long as there is no moisture. I've had my last batch a few months and they are just as good as when I got them.
Up to two weeks is fine to use - it will start deteriorating sooner than that though, which isn't bad, but can be messy looking in bare bottom tanks.
I never reuse leaves - leave one in for a week, I toss out rather than "save" it for another use in another tank down the road. I'm all about the no cross contamination thing lately :)