I rotate about 4 storage bottles, which double up as milk bottles too (Pigeon brand), so usually 1-2 are in the fridge, 1 is being washed/sterilising, and I can use one for pumping. I do sometimes use bags though.. because like you mentioned, I would put the volume that my baby needs for one feed in one bottle. If I have excess, sometimes I put it into the milk bag and freeze it. Sometimes, the milk supply also isn’t good, and I have less than what is needed in the bottle. So I can take one bag out from the freezer to top up. I try not to keep milk in the fridge for more than 36 hours, and I do latch my baby for most of the feeds, so sometimes freezing the milk is needed. I find from experience that it’s important to start bottle training from 1 month onwards, because both my kids rejected the bottle and took some time to be retrained.