You've probably seen other posts about making cute little charms and spell jars, and I definitely don't claim to have started/own this idea. But I would like to point out all the great possiblities acorns have!
Despite being innately lucky magical due to being part of the oak tree, linked to Thor, and other things, acorns really are great things to have around.
For the closet witch, you could easily hide small amounts of your herbs inside hollow acorns. It may not be a large amount, but it is rather incognito if you're like most of us and collect things from nature.
And of course you could make any tiny charm or spell jar you please, and the acorn is biodegradable! Use it in place of glass jars!
"Ah but Rye, the cap falls off so easily. This idea is a flop."
Nay, I say. You just need something to help it stick. A tighter fitting cap may only need a little wax rubbed around it to keep it stuck, a looser one may need some wire, string or ribbon. Glue can be used if you like, or sealing it in wax.
Speaking of wax! Make a wick out of a string dipped in wax, put it in an acorn hull or cap, fill it with wax of your color choosing and have tiny candles! Great for on the go witching, good for your Altoids tin travel alter.
Wirewrapped acorns make fine necklaces! I wear one myself. To make it shiny/waterproof, gloss it over with clear nailpolish.
You can shove a wee crystal in there
If you're really talented with tiny stuff you could even make a super, tiny, tiny alter. Haven't tried that but I like mini things and hey, why not try it out.
Tiny supply holders-have a whole string of acorns or walnuts with different supplies inside. No one is going to look inside your nut.
The Fae would probably like them. Use them for tiny, inconspicuous offerings-caps are plates, hulls are cups
Put an acorn on your windowsill so Thor won't hit your home with a bolt of lightning, I've heard.
You could probably grow seedlings in them but I'm not sure how easy it would be to get them out?
You could probably make a sort of locket with a latch-I may do this, I'll make a how-to post of I do!
Seed bombs!! Super great seed bombs! Just don't glue the cap on.
I'll edit this if I think of something else
Acorns too small? Need something to degrade quickly? Walnut hulls! Hazelnut/chestnut hulls! Peanut shells! Dried pea pods! Bamboo chambers!(Depending on the spell and if you were going to bury it, you could potentially use an array of shells rinds or peels(like orange peels! Or avocado rinds-when dried, they're very hard! And eco friendly!))
Just some thoughts on the acorn, hope this helps you! Feel free to comment your own ideas/any improvements/suggestions!