What’s a Trail Mix Sandwich?

Brett Eldridge tweeted this: "Bout to go out west! Gonna sing songs, go fishing, climb mountains and eat trail mix sandwiches."

He'll be in Oregon, Idaho, Montana, Colorado, Wyoming and California ... every western state except ours! Grrr!

I know what trail mix is, but what the heck is a trail mix sandwich?

Does someone in town make them?