Good for you, Joy. That聮s a very worthwhile event. And 20 miles in a day is聟20 miles. A long walk.
CamelBak Magic Hydration Pack

I聮d probably go with a hydration pack, as that takes care of the water-bottle part of things while leaving room for the other stuff you need. REI has a very sweet little pack out now called the Stoke 9 ($40; rei.com). It doesn聮t come with a water bladder; you buy that separately (get a CamelBak Omega for $28), or of course you can carry bottles. With 550 cubic inches of volume, it聮s trim but has enough room for the things you need to carry, plus maybe a rain jacket (heaven forbid). It聮s highly adjustable and has a comfortable, breathable back pad and shoulder straps.
I also like Ultimate Direction聮s Wasp ($75; ultimatedirection.com), which is just a bit smaller than the Stoke 9 but still has room for the things you need. It聮s very minimal and rides high and close to your back. The straps are very comfortable, so you聮ll hardly know you have it on.
CamelBak聮s Magic ($75; camelbak.com) has the bonus of a women聮s-specific fit, meaning the shoulder straps and waist belt are designed to accommodate narrower shoulders and wider hips. It comes with a water bladder, of course, and has two zippered pockets for essentials. It聮s designed for cyclists but will work just great for a long walk. It doesn聮t come in pink, but it does come in a tasteful light blue and gray color scheme.
Have a great walk! Send us a report afterward.
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