The "filter quests" button which hides completed quests is neabled by default. Just hit the pushpin looking thingy in your diary to see them all.
I leave my stuff in the battlefields, although this only works until you get to the next act. I've read that a good solution is to trade stuff for lighter jewelry, etc., and you can retain most of the value for buying stuff to the next act. Think barter vs buy. The only place where you really need gold is for teachers.
You can use the filter buttons on the left side of the inventory screen to only view categories of items (armor, weapons, etc.), but otherwise you have to clean it up yourself.