If you plant in the fall, the grain will get a head-start before the chilly winter hits. This may result in a stronger plant and therefore a better yield at harvest time (approx. 20%). You also might be able to harvest a few weeks earlier (e.g. July/August instead of August/September).
IMPORTANT: Note that some cereal grains simply won't survive cold winter temperatures (e.g. oats, quinoa, amaranth), so must be planted in the spring.
According to the companion planting bible, Carrots Love Tomatoes, chamomile increases wheat yields (plant 1 part chamomile to every 100 parts wheat). Bachelor Buttons (a flower) aids rye production when planted in a 1:100 ratio.
It should be noted that grains grow 3+ feet tall, and often require little water, so don't expect your companion plants to perform their best given this shaded, dry environment.
1,100 sq.ft. (about 1/40 of an acre) of land should yield 60lbs of organically grown wheat.
1,100 sq.ft. (or 1/40 of an acre) of land has yielded 50-150lbs of organically grown quinoa in the Cowichan Valley.