In the winter, a pair of gloves that keep my hands warm, yet are thin enough for me to still conduct forensic examinations of scenes. They would also have to be chemical resistant, cut resistant and cheap enough to replace.
A bit of a tall order, but useful.
Another device would be to allow clear photographing of bulb filaments, through the glass envelopes, to obtain clear images, without reflection and image distortion. Bulb envelopes are under pressure, sometimes up to 8atm and thus removal of them is quite hazardous and risks the integrity of the filament and posts. This would be really useful.