The contractor bags I've seen are 2 mil. You'll have to go to Home Depot or lumber yard; you won't find them in the supermarket. The trash compactor bags I used in the past were also 2 mil. I would not buy anything less than 2 mil.

Someone told me recently that Hefty trash compactor bags are not scented (after I complained about not being able to find unscented ones), and that they are available in hardware stores. I pass this on for what it's worth--I switched to dry bags three years ago so never bothered to look.