I want to do something along those lines, I want to take the trailers of all the discs I have (trailers for movies I own, not just "any" trailers) and put them together on one disc. Makes it easy to ask someone, what do you want to watch, "here, decide".
If you're trying to make safe copies of your movies (e.g., for young kids to use while you keep the original in a safe place), another problem is that without a dual-layer DVD burner, you may have movies that are too long to fit onto a single-layer disc without additional compression (yuck!) -- many movies will fit on a single layer, though, if you remove the audio and subtitle tracks you don't want.