If you are playing with designing say a backpack which includes lots of different webbings and plastic components, get your hands on a standard glue gun and just stick your bits in place. The glue is plenty strong enough to pull the webbing &  buckles as per a real sewn version.
The glue should allow you to re position the webbing if needed, but beware it will leave a mark behind.

I find this a much quicker way to model ideas and have even been know to use a glued up product for real.

Hope it helps,
Colin