I would like to announce that I have found the perfect stash bag and it's from, of all places, IKEA! Called FÖRFINA, it's not a 100% smell proof but for me it's
IKEA FÖRFINA Tablet case, black | eBay
IKEA FORFINA - 10 Pieces Travel Kit Set | Containers | Bottle | Botol | Organizer Box | Zipper Bag | Fluid | Liquids | Shopee Malaysia