How can I prevent cross-contamination when applying a dry or wet rub to meat?
You can save yourself the waste of making double, while preventing cross-contamination, by using one hand (clean) to scoop and sprinkle, and one hand (dirty) to direct the spice falling, pat/tamp, and rub the spices. 


Typically I begin by applying a "glue" (previously I have used honey and mustard, once I was vegan I went with just mustard; both worked well on smoker) to the cut of meat or vegetable before smoking or bbq. 
I follow applying the glue by washing my hands, then proceed with whatever rub I am using after the glue has had a chance to adhere (typically thirty minutes medium, but I have followed instructions to let set and congeal for up to eight hours). 
Then, you can apply the rub following the method above: keep one hand clean to pick up handfuls of rub and sprinkle the rub down, use the other hand to press that rub you are sprinkling down against the cut.


This sequence minimizes the number of steps, the times where you need to wash your hands, and makes for great bark. Hopefully you can rotate the cut with one hand, if not it adds one hand-wash. I started doing it this way because I hated having the spice turn into clumps from the moisture. Now I not only have no clumps in the spice after, and sanitary spices for further usage, but also a clean left hand for turning on the sink to wash my right hand.