I like my 50l Osprey Aura. I certainly don't fill the entire thing, but I like to have a little extra room for food, supplies, etc. That way I don't have to compress my Patagonia, etc. Whatever size you get, you should have enough room for your essentials (if you're sending a bag ahead everyday) with a little extra for food and water.
Even if you're sending a bag ahead everyday, you want to keep items at a minimum. This is me: 2 shirts, 2 bras, 2 ex-officio underwear, 2 bottoms (1 skort, 1 shorts), 2 pair of socks, T-shirt dress which doubles as pajamas; hat.
We'll be walking end of May so the weather is going to be gorgeous. But it will be chilly in the morning. And it can rain out of the blue. I bring a Patagonia puffy coat and a backpack poncho (see the pic up to the left).
I'm addicted to my poles, but it's totally up to you. I didn't use poles on my first camino, got them on my second, and have used them ever since. I like having them for that little extra pull up a hill, or support going down. Like the bottle versus bladder conundrum, this is a personal thing.
This is totally a personal choice. I am a slavish devotee of the 1.5 liter bladder in my pack with a tube so I can drink all the time. Dehydration is the number one problem on the Camino. Whether you go bottle or bladder - make sure you carry at least 1.0 liter all the time. And there's fresh water along the way - it's a Western country - you can drink right from the tap.
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