I guess one of the more interesting devices was a portable gauge that uses a nuclear isotope to measure the density of soils and asphalt. You've seen the rollers used in road building--there is actually a lot of science that goes into how many times the roller rolls back and forth before the asphalt is at the proper density.
I used to use one of those probes when I worked as a civil engineer. I'd drive a spike into the soil, pull it out, put the probe box over the hole and push the probe down into it. We had to wear these little clips that were supposed to absorb radiation. We'd send them off to DC every week and they would test them to see if we were soaking up radiation from the probes. The carrying case for the probe had all this stuff in it to help you put up a "Do not cross" perimeter if it ever broke open. That tells me it wasnt a trivial amount of nuclear material inside. I'm pretty sure I could have been more safe with it.
We'd use those probes to test the soil under roads and buildings. The guys running the rollers did not really appreciate an engineer fresh out of school telling them that the soil wasn't compacted enough and that they need to keep rolling on that layer.