>>What the heck do you dye?<<
Fabric. Remember my husband and I do historic re-enacting. He has a small container full of them in our garage for when he feels like dyeing something. Most of his 18th century shirts are white or off-white, and when they get too stained, you can throw them in a pot of boiled walnut hulls (no need to hull them though; throw them in whole) and dye them some shade of brown. Walnut hulls are one of the few dyes which don't need a mordant; the dye will hold up well with nothing added to it. Almost every other plant material needs a mordant to make the dye take to the fabric and not fade too much (although all natural dyes fade some). Common mordants are salt, cream of tartar and even iron filings (which themselves color fabric, so you have to be careful what dye you pair them with, but it's a good way to get a mixed color, like, say, purple). We have a fire pit in our back yard, so when we get ready to dye something, we drag out the big cauldron, hang it over a fire, and dye. We haven't yet dyed with walnuts--RIT is our preferred dye--but we have dyed several items in that pot over the fire. It works really well; you just can't do as well in a washing machine or a pot on a stove (I've done both of those too).
The squirrels will eat the hulls of our nuts, but even then, have you tried to crack one of those things open? I hit one with a hammer multiple times and never made a crack. My husband says that walnuts like we buy in the store are from an English walnut tree that makes bigger nuts with thinner shells.