A standard procedure in somewhat-security-concerned firms is that when you travel, you go and get a freshly installed travel laptop (a loaner) from IT dept, use it on the trip, and after the trip, you return it to the department that wipes out everything on the disk and re-images it.

This wouldn't protect against things like firmware-based malware, attacks that major three-letter spy agencies could deploy when they focus on a target, but because there is no absolute security and measures need to be balanced to the threat scenario, this is a model that works pretty well.