I often find myself in a situation where I want to keep an eye on specific crucial resources from different categories - in order to stop using it when it goes down too low or cycle manpower between different production buildings etc. Idea: in the resources area of the UI have a separate tab for "observed resources". Or even better, find a place on screen where they can be visible at all time if possible. Let the player add and remove resources from there by shift(alt? ctrl?)+click on their icons in the resource section of the UI or sth similar.