The easiest authentic topping is fresh made Pico de Gallo, there are lot of variations, but simply:
diced tomatoes, minced jalapeno pepper, diced red or white onion, cilantro, lime, salt. You can add pepper or garlic, and build from that point your own variations.
Sprinkle a little taco seasoning on the meat when you warm it up, heat the tortillas, (I have electric stove), I put the tortilla directly on the burner very low heat and rotate a few times, this gets a little crisp char, and then flip do again. It is slow but adds a little taste.
To give the meat a more authentic flavor, I keep a product from our local Costco in the fridge, a semi fresh tomatillo salsa verde, it is mostly liquid, when I heat the meat I wet the meat with the tomattilo salsa.
(I mentioned heat the meat, when I smoke pork butt, the left overs and there is a lot, are used for taco's or burritos)