I've been hoarding mammoth tusk, horker tusk, dragon bones/scales and was wondering if these are just miscellaneous items used to sell or if I should hold on to them. I know you can make dragon armor but with having smithing up to 100 to use them. I haven't had a use for them yet. Also is there any other miscellaneous items i should hold on to?

There is a quest somewhere for either the Mammoth or horker tusks, I can't remember which. it seems you don't need a lot of the dragon bones and scales to make the armor, so you don't need to save all of them. Check on the Wiki to get more information.

There are definitely a couple of quests that require mammoth tusks. I have not encountered any looking for horker tusks.

There are a few quests where you'll need mammoth tusks. If you hang on to 15 or so you should be fine. Dragon scales and bones are worth saving if you think you will want to craft armor later. Remember, you can make armor for your followers as well and you'll need a few extra for improving. These have a decent sale price though so don't horde too many. Dragons basically never go away so you can get more. As for horker tusks... I can't remember any use for those.

The tusks aren't really worth saving.