StackableItems allows you to raise or lower the default stack amounts for any item. Items can also be disabled (disallows pickup and crafting). Items can be set in three different ways: individual players, permission groups (requires Vault), and universally.

Example use cases:

Carrying 16 snowballs while carrying 64 cubic meters of dirt is ridiculous.
Carry a stack of water buckets or mushroom soup with you so you never run out
Make potions stack
Limit stacks of food for a hardcore survival server
Allow only privileged users to craft/pickup TNT
Allow individual players to craft custom items