I disagree with the previous poster. The OTC Handbook, while very long and overly detailed at times, does contain almost every applicable detail needed for making OTC recommendations in pharmacy practice. in p1 year we have to read the entire thing and i cant imagine there is much else you would need to know. But a lot of information in it is somewhat irrelevant and the authors tend to enjoy taking on a dry academic tone, which may put you to sleep. But if you know the basics, you probably can pick up the rest from practice, as opposed to having to read the whole thing.
The otc drugs and their uses and indications can be picked up on the internet or just by reading the labeling information. I find that knowing about the products themselves is pretty much a no brainer, but it is the key info about exclusions and differential diagnoses that was best found in the textbook. But at the same time, like prazi said, a lot of things (common complaints, how people will present with an illness and finding out what they know about their conditions, medical history, and how to use a product) you can just pick up in the store. Just gotta spend some time talking to people. Spend a single hour in the OTC aisle and you'll be set.