When I am outdoors the last thing I want to take is a lot of extra stuff, the idea is to make life as simple as possible so that I can spend more time letting out the inner explorer in me. Washing dishes is one of those things that for most will require bringing a sponge and some soap. But if you are experienced then you know there are easier ways that require only sand and water. By the way this will also save you money in sponges and soap and these days every penny counts.
What you will need is someplace with a little bit of sand and water, a stream or beach will almost always have both of these items. First scoop some sand into your dish a little water also helps, then scrub until all the food particle are gone. Follow this with a good rinse and check your dish. If it is not clean then repeat until you have it clean. Set aside to dry.
If this bothers you a little bit then put a drop of biodegradable soap in after you have scrub and rinse, nothing worse than having the trail trots because you forgot to rinse well after applying soap.