Everyday Items
Water
Carry water! On some stages there are towns every few kilometers. On other stages you may go more than 20 kilometers without water availability, especially the Caminos from the south like the Via de La Plata, Levante, Ruta de la Lana, etc.
Generally water fountains along the stages are drinkable. You may or may not choose to use them. If you don't use them, you will need to carry water sufficient for the entire day's distance.
There are two primary ways to carry water with you.
Bladders
Refill in the morning. A tube exits from your pack and runs down the shoulder strap to a little Velcro loop near your head. When you want water, you just pull the valve to your mouth, bite down to open it, and suck. Bladders work on the principal of gravity so you have to place them proper side up in order to draw the water. Condensation may get things in your backpack slightly wet.
Plastic bottles
Refill as you need to. Do NOT just toss them aside as trash. Keep the Camino clean.
Cooking in the Albergue
You can have your own community meal even in albergues that offer one. Pilgrims often get together on their own and purchase food items at the local shop, and then set to work in the albergue kitchen (if available) to make their own feast. Aside from being cheaper and always feeling like you are in a restaurant, there is the trail bonding over a kitchen stove and sink.
Washing Clothes
Washers and dryers will not be available at most albergues.
Don't take your clothes into the shower. Period. You're tying up the shower while your wring/rinse, and you will be using up hot water.
The first thing I did at every albergue was the day's laundry to give time for the clothes to dry. If the weather is damp, quick-dry stuff might dry, but heavier materials like flannel will still be damp the next morning. Make this a top priority to give your clothes maximum time to dry. Damp clothes the next morning is just annoying.
I changed outer shirt, underwear and socks every day which means they got washed every evening, almost always in the sink with hand soap and a good wringing. I would switch pants every other day, unless it was particularly hot, sweaty and/or dirty day.
Hand soap worked really well for washing clothes. Carrying specific soaps will probably just take up space in your backpack.
If a washing machine/dryer was available, I put in as much clothing as I could fit.
If you can share a washer/dryer with another pilgrim, you can save money.
Bring along your own large safety-pins for hanging your clothes. The clothes line may not have enough space left for hanging clothes. It might also be worth it to bring along a section of line to substitute if the regular clothes line is either full or outside (and it is raining).