Bacon bits, fried onions, beef jerky.
The Gimme-brand seaweed snacks I get contain oxygen absorbers. So do packages of Tillamook Country Smoker jerky and meat sticks.
They seem to be fairly common with packages of jerky and other self-stable cured meats.
There are both. Oxygen absorbers are used for moist snacks, apparently.
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.