I just put the packs in the washer. Not in the drier. As for my sandals, I have done the same thing, even with casual leather sandals. I just put them in a mesh bag and zip it up.
I usually do this with my sandals when the stink is so bad I am ready to throw them out, but they still look good. Then I am willing to experiment. And the amazing thing is, they usually come out very good. I do make sure I wash them with similar colors, though.