[Kelan]

To clear up a few things below:

The Enormous Cauldron of Broth is actually construction 2, not 6 (based on the Magic Item Quick Reference). The Endless Bag of Wine is construction 4.

Some advantages of the Cauldron of Broth is you can get it quicker research-wise, and in some cases you need to use them. If you put 2 Endless Bags of Wine on one commander, the effect is not cumulative. In cases where your commanders are leading large armies, the Cauldron of Broth can become crucial to prevent starvation.

Another thing that helps supplies a little is any mage with some nature magic. Each point adds some to supply (+5 I think).