Crafting containers can be used temporarily instead of a flask or gourd if none are available!
Gourds and flasks are the only containers as of right now, so some sort of craftable or forgeable container could work as a temporary or even permanent solution. Cheap wooden containers can be crafted with log wedges, dry grass, and sticks. These containers, equal to a flask, have a limited amount of refills as it’s made of wood. The wood will become darker and the cork will be more visible as it weakens. Metal flasks can be forged using a mould that requires a rock plus metal. Durability depends on what is used. A metal container can be also forged that has room for two potions/stews, equal durability but stores more liquid. It would be 2x more expensive than a metal flask if added.
Credit to Edit and Zebulaun:
Sandstone can be used to create flasks too!