Everything. Almost.

I'll go for $20 sunglasses because I lose them constantly and Costco cheap for a lot of stuff because they have enough customer service (that I won't exercise) to think it's not bottom of the barrel, but there's just a bunch of stuff where the money you save by buying the cheap version disappears when you have to replace it.

Specifically in terms of spending more than most would, my ereader is up there. It was like $700 for the discounted "refurb/open box/whatever" version, but it's 13.3" with great sharpness and Android so I can get content from a broader variety of services without jumping through hoops. It wouldn't be worth it for most people, but I've read enough books through it in the time that I owned it that I don't regret it at all (and wish I spent more for the newer version that has a light).