Did the whole thing in sneakers and a t-shirt, although most people looked at me like I was an idiot (but I don't think many people would have been uncomfortable in sneakers). The ice axe came in handy for glisading and for taking the rim of the volcano around to the peak. Snow was really soft even in the morning (I started at 6am).
When I attempted St Helens two years ago, I was thwarted by bad weather and horrendous postholing. This time the conditions were great. I spent over an hour on top admiring the surrounding giant volcanoes and gazing into the crater (and waiting for Ryle). Glissaded most of the way down.