I've never really looked into doing it. How much gear does one need?
Most the stuff you can rent from REI. Crampons, Ice Axe, Tent, Jackelope says best bets to stay overnight to prevent altitude sickness, Which I probably agree with, Its what Ill be doing. Some rain paints for glissading. I hike with them up/down because I get hot and don't like many layers on my legs or I overheat, Then just basic gear, Trekking poles.. Atleast 3 liters of water.
Im sure he can chime in on this in on this in a bit to add to the list.
My problem on St Helens was I didn't take nearly enough water or food. I only had 2-3 liters of water and a few snacks.
Had to bum stuff off people like a bum, and melt tons of snow time after time.
I think going up I drank about 5 liters of water (Two full water blatters *2L each* and a few water bottles) and took in more calories then I do in 2 days normally.