What is silica gel and why do I find little packets of it in everything I buy?

Many of the things I buy contain little packets of crystals. Some of them actually say 'Silica Gel' on them, but many are unlabeled or say something like, 'Do not eat.' I have found these packets in electronics, vitamins and even in some pepperoni I bought last week! What is this stuff? Is it poisonous?
Many of the things I buy contain little packets of crystals. Some of them actually say "Silica Gel" on them, but many are unlabeled or say something like, "Do not eat." I have found these packets in electronics, vitamins and even in some pepperoni I

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