On my Cakes & Dread Goddesses & The Dead, Anon writes:
“In January though, the offering I left for Hecate using the same bowl was still there even the [day] after..I was kind of [disappointed] because I thought the great goddess must have not approved of something in my offering.. The only thing I did different was to add some black raisins in the honey cakes and also used some of the first flour mixture that remained from the first offering. Do you think I should have made a fresh flour mixture? Could the black raisins might not have been favored by Hecate?...Any input would really help me!”
Well, Anon, on the matter of whether you should reused a previously used flour mixture or not, I can't really say. I generally make everything that I can fresh, or I purchase it that day. I would recommend divination if the concern arises again.
As for the raisins:
The first thing to note is, as far as I understand it, the practice of giving sweet fruits, candied treats, and the like was a form of Orphic substitution, eliminating the need to immolate an animal in a correctly made ritual pit. The supper given to Hekate, however, may have predated the rise of the Orphic cults and their methods of “vegetarian” substitution offerings to the dead and Cthonic divinities.
In theory, I see nothing wrong with adding raisins to honey-cakes. They're sweet, and delicious, and you put work into the cakes. That's all solid, and if you were giving it to any other divinity there would probably be no problem. The problem that arises is that evidence has been gathering over the last 15 years (from 1999 on) that raisins and grapes can cause renal failure in a percentage of dogs. The reason for this deadly affliction isn't presently known, though a mycotoxin (or a mold) is suspected. (However, it was never found in the inspected grapes and raisins of the dogs who were adversely afflicted.)
In the cases where you expect homeless dogs will probably chow down on your offering – which is quite fitting – I would advise against using raisins.
Incidentally, you can also consider waiting three days (unless you're concerned the offering bowl is going to mysteriously vanish; I normally just use paper plates and paper bowls, but I don't really check up on my offerings). Unless the crossroads that you're using is heavily trafficked by the homeless or wild animals, it probably won't get taken immediately. I don't think this is so much a sign of the goddess being displeased or anything, as much as the simple low probability of someone or something coming across the chow and enjoying themselves.