Cooking meals at a picnic or on a camping trip, I enjoy. Cleaning up afterwards, I don't enjoy! Here's an idea, though, that my family uses when traveling to make it easier to get the plates, cups, pots & pans ready for the next meal.
Step 1: Hot Water? No Problem.
Since we cook our meals on a Coleman stove, as soon as one of the burners is available, we heat a pot of water (water just needs to be hot, it doesn't need to boil) to use for washing the dishes. By the time we've finished our meal, the water is hot and ready to use.
Step 2: Clean-Up Assembly Line
Most of the time we have access to water for cleanup, but just to be sure, we always travel with at least 1 gallon of water (reusing a Clorox bottle works great for this!). We have 2 large solid plastic bins that nest together and carry miscellaneous odds and ends until meal time. Then, we convert them into the 'kitchen sink' - one for washing and one for rinsing.
After the meal, we start the clean-up assembly line. Add cold water to each basin. Some plastic bins may melt if boiling or very hot water is added first; we've never had a problem by adding cold water before the hot water. Next, add hot water to both basins, more hot water in the bin used for washing dishes, plus liquid dish soap and about a teaspoon of Clorox (helps to sanitize dishes) to this bin.
We usually put the two basins on the picnic table bench seat as seen in the photos, but the edge of the table works well, too. Gather everything that needs to be washed, then start washing, rinsing, and placing on the table for drying, washing the 'cleanest' of the dirty dishes first and working your way through the stack to be washed. If you think you'll need more hot water before all the dishes are washed, start heating more water while washing the dishes, and the water will be ready when you need it.
Everyone in the family or group can pitch in to tackle end-of-meal clean-up and then move on to having more outdoor fun.