A fellow Octopus Overlord posted about these custom-built bookshelves that become the owner's coffin when he or she dies. This is an elegant idea that conserves wood, money, and time spent coffin shopping. The designer says that the coffin is more sentimental for having been part of the deceased's life.
I doubt anyone is going to be buried in one of these except the designer. The family of a deceased person probably won't be in the mood to reassemble furniture. And most people would prefer to inter a loved one in something nicer than veneered plywood.
But if the idea has practical merit, maybe computer desks can be reassembled into coffins. If you're a hardcore gamer whose computer desk has outlasted several of your PCs, that thing probably has sentimental value to you. And when you're buried in it, the coffin can be customized like your PCs were. Give it a window so that your calm face shows through, along with LED lighting of your choice of color.
One can even take a cradle-to-grave approach. When you're born, you get a parcel of wood that's shaped into your crib. The crib becomes your first bedframe, your first desk, your bookshelf, whatever you need as you progress through life. Then you're buried in the same wood. To make things even more environmentally friendly and macabre, the cemetery can collect the methane from your decomposing body for use as energy. If garbage landfills can do this, why not human landfills? Maybe each body in the cemetery can power its own eternal flame (for a while).
Writing this made me wonder whether customized coffins exist. In turns out they're an important industry in at least one part of the world.