Vehicle Supplies: Two extra tips:
1) You can't just drive by a damaged Panzer and kick the supplies out of your M-3 w/o stopping, they will be destroyed. You must stop and kick them out. Also only one of the eight crates is needed for a GV to resupply it.
2) From eihter a goon or M-3, vehicle supplies must be fairly close, I think 800 or less. And remember, they will work for the ENEMY vehicles too ! So the best strtegy is to drop them near the front of the GV battle, but still behind your country's general front lines. You want to resupply only your country's GV's, not the enemy's.