Summary
Crafting containers can be used temporarily instead of a flask or gourd if none are available!
Core concept
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!