So by "disco", do you mean a multi-colored lighted floor, a mirror ball, and John Travolta in a white suit?
Anyway, business as usually until maybe thirty seconds before midnight, then I'll watch the ball drop on TV, then back to business as usual.
I'll also take a sample of air. This is a tradition I started back in '93 for reasons I no longer remember, but I still do it. A liter-sized bottle, thoroughly cleaned and dried, will be filled with air, then the twist top will be coated in molten wax before being screwed on to ensure an air-tight seal, then the whole thing will be sealed in a large Zip-Lock bag that's double over on itself and covered completely in packaging tape, which in turn will be placed in another Zip-Lock bag. The date is written on both the bottle and the outer bag, then it's placed in a box in the closet with all the others. At least, all the others prepared in this way. The two earliest were done differently, they're encased in a large block of ice in the back-room freezer, along with a cookie. I really wish I kept better records back then, I have no idea what the significance of the cookie is.
It's completely insane, I realize this, but as far as traditions go I think this one's pretty well grounded. Besides, I like my more bizarre habits, this one and my sand vial collection probably being two of the strangest. (Wherever I go, I always carry two small vials into which I place sand from the first spot of ground I step on and the last spot I leave from. Sometimes this is impossible and I make due with a stone or some gravel, but I try to get sand.)