Same way I protect 35mm rolls, using suitable sizes of these:
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I use them to store film, fasteners, ball bearings, camera parts, electronic components, you name it. They make great storage for anything small. My friends know to save them for me. I have shelves full of stuff in these.
I carry all my exposed 120 rolls in one of the black plastic bags that Ilford paper comes in. These bags are very tough, light-tight in case one of your rolls unspools (which has never happened to me), lightweight, and cost nothing.
Here's a suggestion that tastes good: you can buy mini-M&Ms in a plastic flip-top tube container that holds two rolls of 120 film. These come in various colors (though the candies are the same regardless of tube color) so you could actually color-code your film by buying appropriate colors.