I think when you take 'optional' items (items that you don't really need but might be useful, ie. the Scrubba), you have to be willing to either carry the extra weight or be willing to ditch the item if you end up not using it. Unfortunately its only after a week or two that one tends to make these decisions and therefore one ends up carrying far too much weight at the worst possible time - the beginning of their Camino!
Why not pack your backpack with only the very essentials and start training with that. You'll soon realize if that's a good weight, too much, or if you can actually add a couple of 'optional' items without any undue stress.
Don't forget - you can buy any essential item in Spain. Maybe not the very day you need it, but most likely within 1-2 days.
Good luck.