A lot! Very bread-and-butter psychiatry, inpatient psych, but the following come to mind:
* Solid diagnostic skills.
* Understanding and monitoring for medical issues of relevance.
* Recognizing what can and can't be accomplished during an inpatient stay.
* Basic and not-so-basic psychopharm, especially for mood disorders and the psychotic disorders.
* Understanding how to implement non-pharmacological interventions, including social interventions and bedside psychotherapy.
* Basic addiction medicine skills, from recognizing and treating withdrawal to medication-assisted treatments, and the first steps in addressing addiction via non-pharmacologicical and psychotherapeutic approaches
* I agree with previous posters that interpersonal skills are important and you're going to have to be able to get along with interdisciplinary colleagues, from social workers to nurses. You're the team leader as an inpatient psychiatrist, so you have to know how to balance leadership and collegiality. I think this last bullet point is likely something that applies to A LOT of jobs in psychiatry and is not particularly unique to inpatient. We all need to be good colleagues and leaders when in those roles.
* And more!