I think Slide is one of the most moderate of the winter climbs and you could go a little lighter than you might for one of the more remote peaks, especially given that you can be sure of not being alone on the weekend.
That being said, you cannot count on the leader to have extra gear for the group, each individual needs to have enough to equipment to survive a night out on the mountain. On this particular trip, a stove, cook kit and sleeping bag might be overkill. In addition to what you wear hiking, I would say you should have a hooded insulated parka, shelled mittens, a balaklava, spare glove liners, a space blanket or bivy sack, a head lamp with lithium batteries, a first aid kit, a 3/4 length pad, spare socks and goretex pants and parka, if you are not hiking in them.
There are many items that could be be added, I would also be carrying insulated pants, an extra set of poly pro, an extra light, a small flask, extra food, an esbit stove with metal cup, a candle, parachute cord, a trash bag, a spare map and compass.
You could probably hike for five years and not use much of this stuff, but bear in mind that if one of your party were to be injured, all of you would be out there for a while, and anyone who cannot sustain themselves could well become another victim. The more people in your group, the more delays you can expect. I like to keep my insulated parka unstuffed at the top of my pack, and pull it on any time I see the group taking of their packs, it makes me a lot more patient. Some one will always say, we're only stopping for a second, and they are usually the first one to get cold, because they make their point by not putting on another layer.
