I have updated Purse of Wonders to include all ingredients from OOO, MMM, and TI (Cobl). Problem is MMM stores it's fish ingredients in an esp. All ingredients that are stored in an ESM get moved/auto-sorted without problems. But the fish ingredients, being they are stored in an esp, don't get moved/sorted. How can I change this so that they do get moved/sorted. I know it has something to do with the fact they are stored in an esp.

Use Wrye Bash to ad a master to your plugin.
Bash lets you add esm or esp's as masters.

Really? By using the ESM/ESPify function?

No, Add Master

Gotcha, done! Let's see if this makes it work or not.

No, it doesn't work. In fact, if I do that, the purse is no longer available in my inventory.

To de-isolate a plugin (that is, make an ESP/ESP dependency) the first thing you need to do is ESMify the ESP you wish for your mod to depend on. This can be done easily in Wrye Bash (right click plugin, select ESMify self). This will make the construction set treat the ESP as if it were an ESM, and allow you to make the changes you want to make.

Two warnings, though:

1. Don't forget to ESPify the master ESP after you are done (and trust me, you will know if you forget).

2. This process will add a LOT of junk data into your mod, so you will need to clean it with TES4Edit afterward.

Okay, I'll try what you suggested.