ItemStack problems

For the part of the mod I am working on now, I need to assign a tag to each unique item, which I am storing in a HashMap at the moment. Originally, I planned to use ItemStacks in the hashmap and assign my tag to that, however due to all itemstacks being seperate that wouldn't work. Using item IDS or the item itself would also be possible, although this would break down when it comes to metadata items as they all share a class/id.

Are there any other ways of saving both metadata and id in one tag, or is there something in the ItemStack that I am missing? Would saving a string of "id:meta" be worthwhile, or are ItemStacks the best option?

Sorry if this doesn't really seem like an issue, but is is confusing me and I am at a total loss as to what else I could try.

Luis