Have you considered portable dry herb vaporizers, which likely reduce smell by >95% or even totally? Plus no matches or lighters needed, no light given off, no fire hazard, vapor is less thick/noticeable vs. smoke, there would be no/negligible recognizable breath odor or on your clothes (compared to smoking; seems something that could easily get you busted), vaporizer safely fits in pocket (even when fully hot), smaller vs. bong, etc. As concerned as you are about security (not getting busted), you definitely shouldn't be smoking smelly bong hits that need a lighter. You could even vape in your home vs. needing to travel to remote locations.
There are some good affordable small handheld units. There are a good number, particularly if things such as stems/mouthpieces are not kept installed, that look very much like most any other handheld electronic device that few would ever identify as a drug paraphernalia, particularly police not themselves users. For ex., any of the Arizer Air model bases or most other handheld simple black tubular-shaped units would fit in with other small electronic devices, tools, etc., and are even less recognizable if disasembled. I will drive across the US in several months and plan to use my Arizer Air Max (e.g., see
https://tvape.com/arizer-air-max-vaporizer.html), keeping it in a box on the back seat floor along with other small electronic devices, tools, etc. These units require battery recharging, which with removable batteries (e.g., as with Air models) you can innocently charge at home.
