Yes, hearts. An item not usually used by most witches, hearts are not only versatile, but also very easy to purchase and work with in spells, curses, and offerings to gods which prefer meat (I’m looking at you, Sekhmet.)
The easiest animal heart to purchase by far are chicken hearts. Easily found in any American grocery store, you can usually purchase 20 or 30 for about $5, giving you plenty to store, and plenty to consume (and they sure are tasty when simmered in chicken broth for a few hours). They’re fairly simple to store and preserve for general workings, as well; you can place them in a jar with a tight fitting lid, and then cover with a 90 proof or greater alcohol like vodka. They may discolor, becoming rather grey, but they keep their shape well and don’t rot. Once they’re soaked in alcohol, they also are a lot easier to light on fire, which can be useful in curses or for burnt offerings. You can also tuck them into salt to dry, much like I do with chicken feet- but since they are all muscle tissue (and dense tissue at that) they are best split in half before being buried in salt to ensure the best preservation- which really defeats the purpose in the first place. You can however, dehydrate them and store them (but chicken heart jerky never has appealed to me).
Chicken hearts are great for spells involving love, or emotional manipulation (the turn of phrase ‘pulling on someone’s heartstrings’ can work in a very literal way), along with curses involving emotional devastation, heart health, or destroying an enemy in general. Since hearts are also edible, you could also treat it as a delicious poppet, naming the heart after your target and consume it (or give it to the dog. Y’know, whatever). They also do well in clay and rag poppets that you don’t mind rotting.
You can also purchase larger hearts at your local butcher or game processor such as deer, pig, or cow. They’re a lot bigger, and as such, are a lot harder to store. If you need a large heart for a large poppet or for a curse, it’s best to purchase them and use them same day. Large animal hearts can be cleaned and stuffed with herbs, paper, stones, or anything else you wish to use, and then kept in a jar or buried until they’ve served their purpose.
This is just a quick reference, and I’ll probably add more specific things at a later time.