I eat a few Fries, put Fries in the Burger, then I switch between Fries and Burger Fries.
After the Burger is finished, lacking Fries around 1/2 through, I finish the Fries off while I sip my drink.
Although sometimes I won't mix the Fires and Burgers, depends on my mood.
Anywho, I suppose I eat the Fires first, and finish them last.