Our house had a leak in the kitchen sink drain and a hole around the drain was cut in the outside siding in order to repair it. I would like to temporarily seal the hole until proper repairs can be made to the siding. What materials should I get (foam sealer, plaster, waterproof paint, etc)? Below is a picture of the hole.
With Winter coming, it is a good idea to insulate around the pipe to prevent drafts, and possible freezing. Since I am assuming that this clean out protruding outside of the wall will eventually be removed, the methods for repair should be somewhat reversible so you can easily gain access to the pipe without having to cut back any more siding.
I would take a batt of fiberglass insulation, and cut off a few strips approx. 6" wide, and then peel off layers of the strips, dividing the thickness in half or thirds which makes it easy to work with. Then you can stuff the insulation pieces all around the pipe. You should add enough to fill the voids, and you can use a paint stirring stick, or a similar tool to pack it in. Be careful not to overly compress the insulation because it loses its thermal efficiency when packed too tightly.
After the insulation is put in, you can take some foam backer rod, and wrap it around the circumference of the pipe to fill the hole up to near the surface of the siding. The hole should also be waterproofed, so you should apply a layer of paintable exterior caulk over the backer rod to completely seal off the hole. You could then paint right over the caulk. If you are unsure what color paint to use, you can take a piece of the siding that was removed to a store that sells paint and have them match the color. Judging by the size of the hole, you would only need a small amount of paint. You can also paint right over the PVC pipe as well. I would also recommend using a good exterior primer since the paint would peel off easily if it wasn't primed. If you are looking for a more permanent solution, you can also use wood putty that is rated for outdoor use prior to painting to smooth it out even more.
As Levi mentioned in a comment, a can of spray foam (urethane) will do the job quickly and easily. It'll last months, at least. I'd use the minimal expansion "window and door" variety to avoid a mess. If you do a careful job that doesn't require shaving lumps later, it'll have a reasonably smooth skin that would probably take paint, too.
Note that urethane foam, caulk, and glue are crazy sticky. They will remain on skin for days and clothing forever. Prepare accordingly.