
Some ideas...
Many grocery and department stores are offering inexpensive reusable bags to make this simple for you. (I've purchased them at both Whole Foods and Target but have seen them at normal grocery stores and understand WalMart is offering them too.)
For more ideas, check out:
Haute Reusable Bags
Knit a Bag!
Feeling ambitious? Make a bag from old bags!
Or go ultra simple. I love the idea of using old plastic bags and turning them inside out, labeling them "Reusable Bag", like this blogger!