It depends on the nature of the work and the work culture.
In most instances, probably best not to discuss anything other than work-related issues, and during breaks not discuss personal issues unless they might have an effect on one's work.
In most places, best not to discuss sex or politics.
1. Your most recent fungal infection 2. Your weekend trip to the state prison to attend a family reunion 3. Where you get all the office supplies that you use at home