Do you really need self-seal bags? Don't the crumbs get everywhere after your child puts the bag back post-meal (don't tell me you have a child who is tidy enough to seal it back up again?). Juice and yogurt spill, apple cores crumble, presumably you can't get away from cleaning inside of the lunchbox, anyway.
Would you consider saving the barely used bags from other forms of packaging? Wrap the sandwich up tight in them? Bread loaf bags, cereal bags, inside bags around the biscuits from Lidl, bags that greeting cards came in, bags wrapped around new magazines. There may be an issue with ink residue on the magazine bags, but you can turn them inside out. Larger bags can be used instead of cellphane or aluminium foil wrapping over leftovers and food in the fridge or even freezer. If you can mange to view every plastic bag or wrapper that comes into your life as potentially reusable, you probably will never need to buy any sort of cellophane wrapping or sandwich bag again.
Would you consider saving the barely used bags from other forms of packaging? Wrap the sandwich up tight in them? Bread loaf bags, cereal bags, inside bags around the biscuits from Lidl, bags that greeting cards came in, bags wrapped around new magazines. There may be an issue with ink residue on the magazine bags, but you can turn them inside out. Larger bags can be used instead of cellphane or aluminium foil wrapping over leftovers and food in the fridge or even freezer. If you can mange to view every plastic bag or wrapper that comes into your life as potentially reusable, you probably will never need to buy any sort of cellophane wrapping or sandwich bag again.