Everything from social network crap, tracking, ads and nasty hidden audio and video ads that hides in iframes hidden from the user.
I thought why not block everything by default. New stuff will not have to be added to a filter list. Allowed content is not changed that often.
1. Block iframes
2. Block object such as flash, audio, video content, animated gif.
If an iframe or object wants to load you can get notified and track them in a list to allow them either permanently or temporary.
I'm getting really sick of these iframes

It would be satisfying to block javascript too but many sites will not work without them today. Dreaming back to when sites were text only, No fancy time wasting animated nonsense. Static menus and dialogs you didn't have to chase all over the screen with your mouse.