I put my TV-B-Gone in an old Motorola cell phone. It was a very tight fit (the case doesn't close as tightly as I would like), but it still looks reasonably like a cell phone if you're not paying attention (and who pays attention to cell phones anymore?)
I admit the flat-head screw as button is a bit cheesy, but I couldn't find anything else lying around that would work as well.
I've seen people selling old (and big) cell phones on the sidewalk in big cities all around the world.
If you can find any cell phone with a battery that works, these are the best batteries for getting very high power from your TV-B-Gone remote (LiPo batteries have extremely high current capability, partly because of their very low internal resistance).
small size and protection of the device are important but Im cheap. I found a toothpick case that cut in half fit perfectly over the component side plus t's flexible enough to allow resetting