One of those big pork loins from Costco.  About 2' long and about 6" around.  I slice against the grain about 1/4" after trimming a bit of fat off.  You get at least 7lbs of good slices for jerky, I think my last batch was closer to 8.5 lbs.  I used two premade spice mix kits, each one was for 5 lbs.  Mad Hunky brand.

Not a fan of that brand!  But spices are the least of my worries when it comes to jerky!

Ive had good experience with Cabela's jerky seasonings.  However, my buddy and I are honing in on our own seasonings.  I think we will get there in 2018 despite how many beers we consume.  We used 9 flavors last practice and were not disappointed with any.  Problem was we didnt document any of those 9 recipes.