Craft an Unfired Clay Bucket from three pieces of clay and then smelt that bucket to get a Clay Bucket. A Clay Bucket can hold water and lava but will crumble in your hands once you've poured lava out.
Clay Buckets can't hold milk and you can't catch fish with them. Use them once and then switch to better buckets or other fluid containers.
Forge vs Fabric
For Minecraft 1.15.2 I have made one version of the mod for Minecraft Forge and one version for Fabric. Pick the correct one.
You can use Clay Bucket in your modpack, but monetization is not allowed.