As the title says, we should be able assign the banners to the formations in the pre-battle screen instead of giving them to companions in their inventory. Banners should belong to the company, not the captain. If a captain's wounded, his banner is inaccessible to the substitute if you forget to switch it beforehand, and if he's killed its lost forever. You may want to switch out a banner for a different one based on the terrain. Pre-battle screen is the best place to manage banners.