I'm new to wood working and I want to build my wife a bathtub tray that can hold a laptop (for Hulu watching) and a glass. It doesn't need to hold anything else really. But I don't know what type of wood to use for this. What wood would be good?!
I would suggest using a hardwood like "teak" as it is commonly used in environments where it is exposed to water such as on boats and for outdoor furniture.
I would suggest a wood that dries and doesn't mold easily. Something like a bamboo or cedar should work well. Also, don't bother polyurethane'ing it, because the coating will just start to peel off with the humidity in the tub.
Teak, finished with tung oil, is beautiful and very humidity-resistant. It is, however, insanely hard to work with. Same for mahogany.
Another option would be any tight-grain, dimensionally stable hardwood, like cherry or birch, and finish with a marine-grade urethane spar varnish. This is a bit more work than normal wood finishing, but the results are beautiful and very humidity/water resistant. The varnish is available from boat supply stores, and the keyword to google the technique to apply it is "brightwork" - the art of finishing woodwork for marine applications.
I built one out of a knotty laminated pine panel, which looks good, was quite cheap, and doesn't warp easily. Coated it with wax, and water hasn't been a problem for it.