As I was digging through the cupboard one morning last week, I found 3 cereals that were really low and I was just really sick of eating. So I took it upon myself to dump all of them into the same bag (which was a nice cereal bag with a plastic closure on it), and I shook it up. It made for a great new cereal and none is going to go to waste.
I think this would also be a great way to use up snacks that only have a tad left in the bag.
It works for me!
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Kinda make your own cereal! Neat!
I do this all the time with snacks and make trail mixes!
The kids love it! 
So much better than 3 boxes each half-empty taking up space.
I, too, do this all the time! And then I fill little snack size bags, so that when we are running out the door to the park or to run errands I can just grab them on my way out.