How Silica Gel Took Over the World

The ones in food are often oxygen absorbers instead of dessicants. They contain iron "sand" that is, unfortunately, not reusable. They're usually very flat and have a "do not microwave" warning on them in addition to "do not eat".

(This is not to say dessicant packets aren't used in food, just that not all of those packets are dessicants)

Can you point to an example?

Silica packets are definitely used in foods that need to be kept super-dry, like seaweed or nuts -- absorbing residual moisture that was in the product during packaging.

I've never heard of an oxygen absorber used in food. A lot of snacks and things (e.g. all potato chips) in airtight containers are packaged in nitrogen so there's no oxygen in the first place.

Are they for small-scale food production that can't use nitrogen? I've never encountered them in my life.