Size 2 Travel Stuff Sack in Pilot Water Bottle Pocket
@jmoz commented that the Size 3 Travel Stuff Sack was too tight a fit in the Water Bottle Pocket of his Pilot. I've found that the Size 2 Travel Stuff Sack is the best fit for this pocket, but it will sit a bit low inside (it's a better fit for the Co-Pllot). While you can also use two small yarn stuff sacks in this pocket, the problem is that with their circular (rather than oval) cross-section and shorter size, you have to be careful not to stuff them full if you want to carry them in the Pilot's water bottle pocket. So the Size 2 Travel Stuff Sack (shown in Solar in the water bottle pocket of the Black 400d Dyneema Pilot) is the best fit I've found for this.