If you keep them out of the heat, AND LIGHT, I've successfully stored even latex gloves for ten years. We're talking 70 degree F longterm warehousing.

In a kit, I'd rotate them every year.
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Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein