What is a simple 8-bit cryptographic hash function that I can use in a quantum simulation of Grover's algorithm?
Your requirement that it not be trivially crackable is already violated by the premise of an 8-bit hash function: for a uniform random 8-bit function it takes an expected 128 trials to find a preimage, and the time for an expected ${\sim}256/n^3$ trials to find the first preimage among $n$ targets if parallelized $n^2$ ways.  But maybe you meant there are no better-than-generic attacks on it.  (Similarly, it takes an expected ~20 trials to find a collision, although it's not clear that collisions are relevant to your application.)

You could use a Keccak sponge with 1-bit words for a total 25-bit state, 12 rounds, and an 8-bit capacity.  I don't know 25-bit Keccak admits better-than-generic attacks—I wouldn't be surprised if it did—but it is structurally the same as the Keccak permutation used in SHA-3, with 64-bit words, 1600-bit state, 24 rounds, and either $4\lambda$- or $2\lambda$-bit capacity (respectively, for the fixed-size hashes like SHA3-256, or for the extendable-output functions like SHAKE128) for $\lambda$-bit collision resistance and $2\lambda$-bit preimage resistance.

Right now, the best collision attacks on 1600-bit Keccak[1][2] seem to be limited to 6 rounds, which justified the use of 12 rounds for KangarooTwelve.  There are newer attacks on other aspects of Keccak, but 12 seems like a reasonable margin—and it's not clear that those attacks would be cheaper than Grover.  If all you want is preimage resistance, a $\lambda$-bit capacity should suffice for $\lambda$-bit preimage resistance.

One nice thing about a permutation-based sponge like Keccak is that the fixed permutation is, well, a permutation, so it will require no ancillary qubits to implement; the only need for ancillary qubits will arise from xoring the message into the state to hash it.