Fajitas: Marinade Vegetables With Chicken
Your grocery store has it down to a science. 

To get all parts "done" at the same time, they have to be cut to the right size. Your grocery store does that very well. The marinade flavors all parts, but the marinade doesn't carry flavors much (see here, different but similar: How deeply will the flavors in a brine penetrate chicken?) So it works.

Is it safe? Certainly, as long as you cook it within a couple of days and don't let it linger in the "danger zone" (40F to 140F) for too long. (Too long per government standards is 2 hours cumulative. Since you can't know how long the grocery had it there, don't mess with it, just put it in the fridge as soon as you get it home, and cook it straight from the fridge.)