This includes a patdown and anything he can touch quickly. I.E. under the seat, the glovebox, etc.
It generally does not include zipped up backpacks and certainly not a locked briefcase where a person has a "reasonable expectation of privacy".
Always refuse a search but do not physically interfere when it occurs anyway.
For more details see "You and the Police!" by Boston T. Party.
Probable Cause is another matter.