i should have added---silk thread although wonderful thread- is quite expensive & i would never (waste it) on constructing a tote bag- those of us who tend to use alot of silk threads generally use them for applique- and sometimes for very special quilting.
often when making and quilting quilts we use 40-60 wt thread- long arm machine(ers) tend to use aurafil & polyester threads- the machines go very fast & cotton thread breaks easily- but cotton works well often when quilting with a domestic machine.
i piece with cotton most of the time - poly for totes/purses/ table toppers, runners/ items that will be used, abused & laundered often- applique with silk and quilt with polyester or aurafil...but that is just the (general) way i do things- i may do things differently from one project to another- i've used lots of (specialty threads) metalics, invisibles, rayons, what ever suits my project.