Premix goes in the Jeep. Some people won't run it in their cars, but I have done so for years and (knock on wood) have never had a problem. A gallon or two mixed with 15+ gallons in a truck tank gives you a huge premix ratio.
1 gal of 40:1 mixed with 20 additional gallons of gas gives 640:1. Heck, I've run my Jeep on basically straight premix when in a bind before (almost out of gas, had 5 gal of premix, voila, no longer almost out of gas. That trailhead was way farther out than I planned for!).
As for transmission oil, most auto parts places will dispose of oil for free. Back "home" in Michigan there were tons of businesses that would take it to burn for heat in their oil furnaces.