Favorite coffee and favorite yarn. That's like asking a chef "what's your favorite food" or a literary critic "what's your favorite book". In some ways, it's dependent on the season, on my current knitting interest and also just what I feel like on a given day. So, for this contest, I'll substitute "favorite" for "guaranteed to please"!
In the coffee department, should I end up stranded on a desert island and can only have one bag of beans delivered, it'd contain these:

Peet's Aged Sumatra. This stuff is absolutely heavenly. Lots and LOTS of flavor but very low acid so it's totally drinkable. Because of the mildness of flavor, it's definitely *not* suited for the rigors of espresso-making. All the best qualities of this bean come out using a drip or filter process. Yeah, Sumatra. Always a winner.
Ok, let's move on to yarn. Generally, I'll choose some flavor of sock yarn since socks can be knitted anywhere, anytime, and offer nearly endless possibilities for patterns and shape and size. They're the Swiss Army Knife of knitting. That being said, there are plenty of amazing yarns out there -
Curious Creek,
Koigu,
Natures Palette. However, after stalking one particular supplier for well nigh on a year, I finally had a package show up on my doorstep that contained this:

Yes, friends - this is
Wollmeise. A wonderful husband and wife team (husband does custom ironwork!) in the south of Germany that make the most delicate, squishy, colorful and truly *touchable* yarns. Her range of colorways is amazing ... if my stash contained nothing but her yarn, I'd be a perpetually happy knitter.