Grocery bags are free.
idk about you all but I find that over the course of 3-4 days of vacation we can use a nice portion of a pack of garbage bags, and it's much simpler and more convenient than being busy with small shopping bags.
But then that might not be a hack
Here's my life hack: stay in hotels with a walmart or target close by, and then instead of shlepping waterbottles, garbage bags
, even possibly produce, and anything you forgot to pack, just buy it there.