I mix [heavy cream powder] and powdered milk in equal portions to make half-and-half that I can keep at my desk without refrigeration. I keep it in [baby formula dispenser]s so I can shake it up for homogeneity and dispense it without digging in with a spoon.
[heavy cream powder]: https://www.amazon.com/Anthonys-Fillers-Preservatives-Friend...
[baby formula dispenser]: https://www.amazon.com/Philips-AVENT-Powder-Formula-Dispense...