American management teams are made up of members of unequal rank. Depending on the nature of the work some disciplines might be more important for overall success than others: such as product development or manufacturing or sales/marketing moreso than accounting/finance, human resources or health/safety. And within product development, design engineering might be more important than testing.
Some team members may have more power and influence due to their experience or record of producing excellent results. Then there are others in the management team who enjoy a high level of influence based on their personal relationship with the team lead, a relationship perhaps built up over years of close collaboration.
The term kitchen cabinet refers to those team members who have a special relationship with the team lead. The kitchen cabinet might also include people from other parts of the organization, such as a senior-level mentor to the team lead.
Kitchen Cabinet was a term used by political opponents of President Andrew Jackson (1829-1837) to describe the unofficial advisers he consulted parallel to his cabinet. It was said that Jackson would meet formally with his cabinet to discuss important issues of state, then meet informally afterwards with selected, trusted advisors in the kitchen of the White House to discuss more openly and critically those same issues.