You can set a quantity for a resource, and allow that resource to be assigned to multiple people. This is ideal for situations where you have a large quantity of a single type of resource that you do not need to track individually (e.g. provisioning staff with uniforms).
When creating or modifying a resource, select 'Allocated to' -> 'A person', and then select the 'Allow multiple people to be allocated' option, and enter the amount of stock that you have for the resource.
You will then be able to allocate the resource to multiple people. The remaining quantity for the resource will decrease by 1 for each person you allocate, and when it reaches 0, you will no longer be able to allocate the resource to additional people. When a person is removed from the allocations for the resource, the quantity remaining will increase.