If you get good at the lettering it becomes almost a textural part of the sketch. Soft goods can be challenging. The important thing is to think through the details. Soft goods are basically 2d sheet materials that are folded into the 3 dimensional goods. Things like stitching, seams, pattern breaks are much more important than wrinkles. I tend not to draw any wrinkles in my softwoods because I find them distracting, but I know other designers who do it really well. Bellow is one of my bag examples.
See how things like stitching and just a subtle simulation of materials using the marker to stipple give it a little believability? Also notice that if you take all the graphical and material break ups away, it is a very simple construction. A front panel, a pleated life panel, and a back panel that wraps over the top.
