Hi, Alex,
Personally, I haven´t attempted to model a bag, but with all that great stuff posted here - and I remember seeing something about shoe modeling also - I believe it is quite possible to design bags in SU as well.
This may come in handy for pushing/pulling bendy and curvy shapes http://forums.sketchucation.com/viewtopic.php?p=42783#p42783
And you also shouldn´t miss this one http://www.smustard.com/script/SubdivideAndSmooth
Oh, and welcome to the forums!