The supply system will suddenly order billions of gc worth of unnecessary supplies for your country unless you tweak it, and even then it will sporadically flail like an epileptic on crack and order some products spontaneously. Check supply stocks every so often to sell off super-surplus supply. Also, if your country has a lot of corps affected by recent supply fairy shenanigans, those corps will suddenly start hemorraging like a hemophiliac in a piercing salon.