A few more rough ideas based on your suggestions:

Shovels & Rope Apparel concepts

Here are a few rough ideas for apparel graphics:

A southwestern inspired thunderbird graphic - bold lines and bright colors. 

I've been really into the sort of cheesy tour shirts that people were doing in the 90s (example here). I thought it could be cool to do a goofy throwback to that look, we could even make the print look a bit weathered and cracked to really nail the goodwill aesthetic. 

An Invisible Man, fading away... 

Vintage racing inspired, shovels & rope meets 70s nascar aesthetic. This one could be really cool as a pocket print too. 

Drawing inspiration from blue collar shop t shirts, an old school auto shop look complete with catch phrases, an address, phone number, services offered etc... This could be a cool back print paired with a pocket print on the front. 

A severed snake head framed by some classy laurel and other graphic elements. Very tough!