I have a heavy-duty storage box on the rear bumper where I keep my sewer hose. I can stuff several days of garbage in there when necessary. My boondocking policy is 'short stays only', e.g., four days or less in one place. When I stay longer, I have to drive out to take on water, dump my tanks and dispose of garbage and then return.
In Alaska this summer, I found one of the most difficult issues was garbage disposal. Even some of the state campgrounds didn't have trash bins and many of the dumpsters in the towns were chained and locked. OTOH, BC had trash receptacles every few miles.