Sometimes you need to be able to measure some basic information, but don't need those measurements to be particularly accurate
Many Android phones have four sensors that can be read by apps, however not all sensors are present in all phones:
An ambient light sensor, usually used only to automatically adjust the screen brightness.
An ambient humidity sensor.
An ambient pressure sensor, used to supplement the phone's altitude measurements.
An ambient temperature sensor.
Reads all available sensors:
If you have a meat thermometer, many of those are capable of working as an ambient temperature thermometer. Just check its specified temperature range to ensure it can also read lower temps. Optional: crumple up a small aluminum foil ball over its tip.
You could keep a few thermometer strips on hand, as they're cheap and very compact.
To measure the direction and magnitude of airflow, you'll need a smoke generator. Then, observe which direction the smoke drifts, and roughly how quickly it drifts away.
Apps that guesstimate length using the camera:
Apps that will display a mostly accurate ruler on-screen:
Similar measurements: