Sometimes I listen to my mp3s, sometimes to to my spc collection (Mario Paint music is awesome to pixel to). I hook up my wireless headphones because I work in spurts; I'll grind out two hours, then get up and walk around for a minute or two, so that I can refocus my eyes and come back with a fresh look at the piece in front of me. If I have multiple projects sometimes I'll just switch between them, but usually I walk around, mess with my dog, come back, check the forum/channel, IM people, etc before I get back to work. Helps it stay fun if I remove some of the pressure. Once in while I'll take a break to emulate or netplay on an emulator with a buddy. Most of the drawings I squirt out are done within 2-3 hours, so if I work uninterrupted longer than that I start to burn out.
I have a big CRT monitor, an LCD tablet (screen calibrated to the contrast of your typical mobile phone), and a TV, and I have magnified previews on the two I'm not currently pixeling on so I can preview for whichever platform the art's targeted for.
I usually either drink Cherry Coke or whole milk (<3), and when I get hungry I typically eat meals while I work too. I don't smoke cigs anymore, but I am known to roll a blunt during long work days (don't do drugs, kids). Sour Apple is best.
I also find it impossible to work when I'm hungry, and trips to the store are not an uncommon precursor to a work session.
I don't have a preference for light or dark when I work but if the lights are off when I start they're going to be off until I get up and walk by a light again, so I find myself working in the dark a lot. I don't really bug other artists with progress shots often because as you may be able to tell by the frequency with which I post art I don't care about other people's opinions as much as I should when it comes to my own art :p Clients and supervisors are a different story however; I can't stand revisions, paid or not, so I spam them with milestone shots every chance I get.