If this were a job interview, then I'd say "put the spare bags in with the laptop"... Or the "bag" can be the laptop's existing case. You can put seals (sticke

If this were a job interview, then I'd say "put the spare bags in with the laptop"... Or the "bag" can be the laptop's existing case. You can put seals (stickers, or the sparkly nail polish trick mentioned below) over all the fasteners and seams of the laptop, fill all the non-power ports with epoxy, etc. None of these make tampering impossible, but they can make it uneconomic. I don't think anyone at serious risk of these kinds of attacks lets computers out of their physical control. I've seen agencies that do the seals/epoxy even for computers inside their secure facilities, presumably to give their guards more time to catch an inside tamperer.