Must a uniform be worn to drive/ride in a CAP van? If so, by driver and all passengers?

There is no specific requirement for senior members to be in uniform while driving or riding in a CAP van unless they are participating in or conducting the cadet program. Note: The wing or region may have established such a requirement.

CAP uniform wear is required by all while participating in or conducting the cadet program or flying in CAP aircraft (corporate and member-owned aircraft used in CAP flight activity). If cadets and seniors working with cadets are traveling in a CAP vehicle while participating in the cadet program, they normally should be in uniform. However, the regulation does allow region or wing commanders, or designees (usually group or unit commanders), to prescribe the type clothing to be worn by members while flying or engaging in organized recreational activities. In this case cadets might be authorized by a commander to ride in CAP vehicles wearing civilian clothes. For example, during a volunteer clean up day or trip to a theme park or unit picnic or other social gathering, all CAP members would likely be in civilian clothes.  See CAPM 39-1, para 1.2.4 for more detail