I'm with everyone else here, I have pretty much every slot filled with the bigger bags. (I also have a spice rack and element bag too.) It makes it a lot easier to collect things through a game day.

What I like doing with my old smaller bags is leaving them on a random street in Ur for someone to discover and maybe use.

I'm also seconding the 'donating spare stuff to shrines'. Especially when it's resources that you get img for when you collect them. Like piggy meat. Shrine donations are handy because once you hit a certain point, you get an emblem - and your first emblems will unlock further skills - and those can also be used to speed up learning time.