mbart,
While I was on the del Norte, I didn't notice much abandoned/donated equipment on the first two to three stages. After that point, I started to norice more and more equipment left behind. I would imagine that the equipment that gets left behind would be a function of injury or realization that something wasn't worth the pain of carrying it. I started in Irun on April 28, a little over three months ago. It was supposed to be the rainy season still. The night before I left the pension in Irun, it was raining in torrents and cold. Pilgrims went by my hotel (Bar Pension Restaurante Bidasoa) as I looked out the door from the bar, the occaisional pilgrim would stick his/her head into the doorway to get out of the rain for a few minutes, grab a cup of cafe con leche, ask where the Way was (the sidewalk right outside the door) and press on. I was so glad I brought my rain and cold weather gear. As I left the hotel the next morning, the sun was out, the sky was clear and the long sleeve thermal shirt I was wearing was way to hot. From then till I finished, I had one day of light showers for the next 39 days. When I got to Bilbao, I sent home tent, tarp, sleeping bag pad. By the time I got to Comillas (for me, Stage 14), I sent home my cold weather gear. For the same time frame, start to finish, the temp never got below the mid 50's F or above the high 60's F. About the same time, or slightly before, I donated my trail sneakers. My feet had spread out enough on the camino that they no longer fit, and were the footgear I wore on Stage 1 when I incurred most of my injuries.
The long and short of it is, in my opinion, the items left behind are a fuction of anticipation versus reality. As the old saying goes: Too soon old, too late smart. In the second half of my del Norte, it was get up, dress up, gear up, the same equipment every day (Vaseline, socks, shorts, boots with removeable over the counter orthotic pads, short sleve base layer T-shirt, hat, sunglasses, trekking poles and rain jacket outside of backpack readily available, filled water bottle up front.
On my next excursion, my gear list will be different than the first one. I will take a set of rain gear, but much lighter. No tent, tarp and pad except during the high season when a bed my not be available (I started and finished before the high season). Cold weather gear will be what I have normally now, but lighter and in more layers. One pair of footwear, new but properly broken in (1 1/2 sizes larger than my normal shoe size now) with SmartWool socks.
Anemone, everybody learns from the first camino. That learning curve is much steeper on the del Norte as opposed to other caminos, especially the first half dozen stages. The steeper the curve, the more the equipment
Gets left behind/donated.
I did a practice overnight camino, with all my gear, to a campground I frequent about 50 miles away. I rode a train to about 15 km from the campground, and hiked in and out. I found out the sleeping bag I had was not going to work. Trying to go through my gear in the tent in the morning taught me what I later found out to be true on the camino; it's impossible to get ready for the day without making a lot of noise. Too much small gear, headlamp, tooth brush, sunscreen, packing backpack, sleeping bag, getting dressed, etc. at some point, you finally say "do I really need this?". Your feet will tell you, and you too will become a donor of un-needed gear at some point.
Take what you need, buy what you want. Above all, protect your feet and legs.