Lug-a-loo bucket with lid/seat and two draw string kitchen bags. Tie it up tight and toss it first dumpster I find. This is my emergency facility when not pulling the 5er. Used plenty of times in the van, on the boat, at the beach, etc.
I tried dumping down a RV dump station ONCE without using the bags and while that is possible it is not pleasant. The double bags keep all the odor inside if you twist, knot, and tie each one.
I have heard that using some kitty litter in the bags helps solidify the waste but I have not tired that yet.