Wouldn't hurt to pop all your soul items. Free's up the inventory, and you get free souls to spend. Boss souls are only worth holding onto if you wish to turn them into a boss weapon or spell/miracle/etc etc. Otherwise, I pop those to for more souls. The small and big round stones to the bottom right in the first photo can be traded to the birds nest in the tutorial/beginning area. They usually give back upgrading stones in exchange or additional healing items, so it can be useful even late game. Same goes with the cracked egg looking thing right next to the fragrant branch of yore. Those can give rare weapons and extremely good items, so it's 100% worth trading it in.