Yes the Whippet is a self-arrest tool used for ski mountaineering. Not something you would want to rely on as an ice axe, but in emergencies it might help arrest a fall.
As for pack size, that obviously depends on the plan of the hikers/climbers. Since you were doing a one-day trip obviously your pack will be much smaller. For someone taking two or three days to acclimate and go at a leisurely pace, the normal demands of a tent, stove, extra food, bag, etc. will obviously dictate the need for a bigger pack. Of course it's up to each person to decide how they value comfort vs. weight, as long as it doesn't compromise safety.
