The silica packets in pills, shoes, beef jerky, etc. have normally absorbed all the moisture that they can. You can but silica gel at hobby stores for drying flowers and such. It's really cheap and can be re-activated in the oven.
Just make sure that the silica doesn't touch the pollen/seed you are storing. I put a little layer of those silica crystals in the bottom of a clean mason jar. Then I put the pollen/seed in a film bottle without the cap and place the whole thing into the jar. After about a week or two, you can just stick it in a zip-top bag and store it in the fridge.
