A couple of other solutions besides Adox canisters and DIY bodged-together 35mm ones: One of the standard or common sizes of plastic pill jars handed out by US pharmacies is ideal 120 size. I have a family member who is on a medicine for life that she gets in jars of that size, so I have unlimited supply. (Another common size is same diameter, but taller, which would still work albeit with some rattling about of the film.) Remove labels, spray-paint black, and you're ready to go. And they've got child-proof caps! So if your toddler gets at your kit bag, maybe that stops her opening your 120 films to the sun. 
There are also black nylon (?) bags. I have a thin one that holds about 15 120 films (if unboxed). I believe it is the leftover (so, "free") carrying bag from a laptop computer locking cable. It is a slightly loose weave so probably not 100% light-tight, but surely provides more darkness than if I left the exposed films naked, and saves the weight of individual canisters/jars when I'm weight-constrained (hiking, etc.). I use it in replacement of the film/miscellany pouch that came with one of my camera bags. That pouch is an even looser, almost translucent weave in light grey. Who thought of that?!
--Dave
There are also black nylon (?) bags. I have a thin one that holds about 15 120 films (if unboxed). I believe it is the leftover (so, "free") carrying bag from a laptop computer locking cable. It is a slightly loose weave so probably not 100% light-tight, but surely provides more darkness than if I left the exposed films naked, and saves the weight of individual canisters/jars when I'm weight-constrained (hiking, etc.). I use it in replacement of the film/miscellany pouch that came with one of my camera bags. That pouch is an even looser, almost translucent weave in light grey. Who thought of that?!
--Dave
