I rarely use the microwave. I prefer the taste of food cooked and even reheated on the stove or toaster oven/oven. There are a few times I do use the microwave, though, and I don't cover the food. Like someone else said above, things that splatter generally do well on the stove.
I clean out the microwave with vinegar/water (50/50 in a spray bottle with a rag) once a month and wash the rotating glass plate in the dishwasher at the same time. On the rare occasion something does make a mess, then I use a rag with the vinegar water or soapy water (if it is already available) to clean it out.
Plastic trash bags alternatives haven't come up for us yet. We reuse the grocery sacks (paper or plastic) several times because I feel washing the cans out is just as bad environmentally in our drought conditions. We use cloth bags mostly (even for non-grocery stores), but still end up with enough plastic/paper to handle our trash load. We only empty them once a month or less and they are not overflowing. We use the kitchen trash for icky trash and we use a repurposed box for recyclables. We change the bag only when necessary. Otherwise, we simply dump all the stuff into one bag or box (from something else already going out) or take it directly out. DD (age 7) handles all the small trashcans in our house under our supervision. She can take some things out to the dumpster herself (bags or boxes smaller than her), but she cannot handle emptying a can with a bag inside due to her height and dexterity. She can empty the recycling box while retaining the box simply because the outside bin is shorter than she is and she (we) stand there and sort the paper-type items from the glass/can/plastic type items with the box on the ground. I may eventually buy a two-bin system for inside the house to presort, but the repurposed box serves its purpose nicely without spending extra money OR adding more permanent stuff to our home. It also forces us to take it out frequently.