What is the abbreviation for Enclosed With?

There isn't a standard abbreviation for "Enclosed With". However, depending on the context, you could use:

* Enc. or Encl. for "Enclosure" or "Enclosed"

* W/ for "With"

For example:

* Enc. W/ brochure

* Encl. W/ invoice

It's always good to be clear and concise in your writing, so choose the abbreviation that best suits your situation.