For really sensitive applications like voltage references, they actually build a little enclosure around the part with a built in heater to keep it at a constant calibrated temperature. The boards also often have cutouts to reduce thermal transfer and things like the board flexing causing stress to the part.

The resistor itself won't really drift at a constant temperature, especially in a sealed environment where condensation, corrosion, and dust aren't a factor.

As a layperson, what happens if crumbs from my sandwich fall all over your chad experiment setup?