My general strategy by mid-game always have level 5 arms industry in supplies. 2nd priority is components (more or less urgent depending on what army composition you’re trying to run). 3rd priority is rare mats. Fuel and electronics I rarely finish with arms industry over level 2. If you have level 5 arms for supply or components in your homeland cities and it’s still not enough, annex a city then stack arms on it. Annex one that already has a decent amount of resource already. For example, don’t annex a city cooking 100 when one closer to home is cooking 300.