Grizzly bears will eat just about anything, but I would think a nice fat salmon & some nuts & berries would produce their best shit. Hope that answers your question.
That's a tough one honestly. I'm a big fan of all of their albums. I'd probably start with Veckatimest seeing it's their most straight forward album. Then Yellow House followed by Shields. Horny of Plenty is great but that's when it was just Ed Droste in his bedroom making music and not a full band yet. Both of the EPs are worth grabbing too.
I wouldn't even say the order I told you in is how I rank the albums but it would probably be the best way to check out their music in my opinion.