I like to contain as much sawdust as possible, even when cutting outside at clients’ homes. The discharge port on my tablesaw collects most of the dust, so by attaching a bag I don’t have to sweep or rake up the mess.
A large plastic garbage bag makes a good collection bag. Just tape up the open end, except for a few inches on one side. Roll a piece of coil stock to friction-fit around the discharge pipe and tape it to the remaining hole in the bag. Then poke several holes near the top of the bag to let the air escape when the saw is running.
Some dust leaks out of the holes, but it’s minimal. Most dust settles in the bottom of the bag.
I’ve found it’s best to only let the bag get half-full before swapping out for a new bag If it gets too full, the discharge port may plug up with dust and then nothing flows. Remember to save the coil stock adapter—it can be used on the next dust collection bag.