Okay just a little tip for things such as powerfishing/mining/etc. I'm sure a lot of you probably know this already, but if you are trying to drop a set of the same item out of your inventory, simply drag one of the items (i.e. a salmon) onto a spot on your action bar. Then, spam the hotkey for that action button and they will all be dropped. Try it out!
If you simply hold in the "9" key, it will drop your full inventory of trout after about a second, and then just hold in the "0" key, and it saves you rapidly hammering the keys.
Edit: Okay here is a picture. In this instance I am speedfishing with fly rod and salmon/trout. So I drag a salmon and a trout over to two action bar spots, and then when my inventory fills up, I rapidly smash 9 and 0 on my keyboard to drop everything in under 2 seconds. Enjoy