which antibiotics do I use

I have not had to treat any of my hens yet, but would like to have meds on hand (because you know it will be on a Sunday night when they get sick.) Can anyone tell me where to find a list of meds for treating the most common injuries/ailments? I keep amoxicillin on hand for the cats but would not know the dose for a chicken. I prefer to treat organically, but a good antibiotic is always handy.
Thanks