I've realized that when I have foods of different quality, the system uses the higher tier first. This doesn't help with the storage and the game has no option to change that.
So my suggest is to add an option in settings or somewhere that I can force the game to use the lowest quality food first, so it would use 1200 Q1 food instead of , for example, 400 Q3 food. This would be more convenient as it would leave me with 800 more space at the end of the day.
I had a lot of trouble because of that. I had many donations as I am a new player but then I couldn't buy things because of the limit. And seeing that it only used Q3 food was extremely frustrating. I had to wait 20 hours to buy something and I couldn't sell items to free storage as the option was disabled because I was new (I think it was because I had low Strength)