Many grocery stores encourage customers to bring reusable / recycled bags with them when they shop (e.g. Trader Joe's and Whole Foods).
Recently, when I was looking for my reusable bags, it occurred to me that my suitcases typically sit unused in my closet. And these are the ultimate reusable bags. They're intended to be durable and easy to move. Instead of using grocery bags, I've started loading my groceries into suitcases. Granted, this is a little awkward during checkout. But, as long as you're willing to load your suitcase yourself, the cashier isn't going to complain.
Using suitcases allows me to carry more groceries at once. As a result, I no longer need to take multiple trips up and down the stairs. This is more efficient and more comfortable. And as an added bonus, it's also better for the environment.