Edit: Well, it looks like i was mistaken. As can be attested to by numerous other players, items do in fact auto-stack in your inventory. Hence, my suggestion is moot.
As many of you have surely noticed, stacking items (such as health hypos, shield charges, and power cells) can be extremely tedious. Unfortunately, they just don't stack automatically. Therefore, they take up way too much inventory space, even though you may have a stack of 2 and a stack of 3. Why not just have it so that when the item is acquired, it automatically stacks to existing items. For instance, in the example above, if you already had a stack of 3 small hypos, obtaining a stack of 2 from a corpse would create not two distinct items in your inventory, but instead add the 2 new ones to the 3 already in your possession, simply making it a combined item of 5 small hypos. This seems like a no brainer for me, and I'm not sure why it hasn't been implemented. In any case, this is such a simple request that it makes no sense not to be included in the next patch. For those that agree with me, please post your support here!