|I would like to know which types of vegetable plants will do best in zones 8-9, grown in straw bales.|
|You should be able to try any type of vegetable (except perhaps corn), since the bale is just a big container. Since the plant roots can't spread very far to seek moisture and nutrients, you'd have to keep an eye on moisture levels and any sign of deficiency, such as yellowing leaves. If you've never planted veggies before, here's a helpful publication from Oregon State University. It lists planting dates and best varieties for your planting region. Even if you have gardened before, it's a handy reference!
Best wishes with your garden!