I have the Japanese modern fleet in 1/3000 ready to paint but that is a small task and really will be a filler between the early Soviets being completed and the next 6mm project. One option is to finish off the Soviets with mid and late World War 2 troops. This is the lead-pile ready for that.
Lots more AFVs – 20 or so T34/85, 10 JS-2, KV-2s, more KV-1s.
Also more artillery, Katyusha rockets, some later war aircraft (Yaks) and a bigger artillery battery or two.
Lastly, in case one finds oneself near a river, some floating vehicles would be useful so we have some boats 🙂