I also wanted to give an offering of olive oil and barley, and luckily we had both in the pantry. I set up a small shrine to Her last night. It looks like this:
You can see the oil and barley sitting on the left; I later poured these into the white dish. The back of the altar is adorned with some paintings of mine, as well as several owl images, a few things I've crocheted, and some of my pottery. I put some knitting needles and a crochet hook in one of the pottery pieces. Also present is a tea light, a replica arrowhead, and an award from my high school.
I wore the flower crown I bought at Fairy Fest, as well as an owl ring, and a red shirt. According to Judika Illes' Encyclopedia of Spirits, red is Her color.
I had worried that I would not receive a response, but no sooner had I finished introducing myself and giving the offerings than I received an image of Her in my head. She spoke to me for some time, and one of the final things She requested was that I share the knowledge of her power. So - if you are feeling in any way drawn to Athena, then make yourself known to Her! She accepts all honest acts of devotion.
Here's a closer look at the back of the altar:
