Organic free range eggs. They are 5 euros a dozen as opposed to the 1 euro a dozen of conventional, and we are poor students, but I will never buy conventional because they are just anemic and tasteless (and inhumane) compared to the free range organic ones.
Organic honey. DP never liked honey until I introduced him to organic raw honey and now he absolutely refuses to buy conventional.
Organic/wild meat. We decided we just wouldn't eat conventional anymore for ethical and health reasons. This has resulted in me now trying to learn how to identify and prepare cheaper, less well known cuts of meat because it's way too expensive for us otherwise.
Organic cultured butter when we can get it

That's the one I have the most trouble with though - it's 10 euros a pound compared to the 1 to 4 euros of conventional

And we also go through it fast.