I bought ours at Walmart, 3 bags for $6 which I'm sure aren't environmentally friendly made. Amazon has some great ecobags:
They also have a pack of 5 100% cotton bags for $19.96 100% Cotton Canvas Grocery/Multipurpose Tote Bag 5 Pack, Shoulder Length Handles which is great if your doing this with a playgroup like we did! Since we were making 3 bags for just us, the Walmart 3 pack worked out fine.
The supplies you see here are: Wipes to get the paint of ASAP - it dried very quickly onto your hands so wash off quickly! Fabric markers, Fabric paints, Paint brushes, T-shirt, and Canvas Bag
I painted the kids hands with the fabric paint and arranged them like a garden on the bag.
I did the same with the t-shirt. I lined the bags and t-shirts up in a sort of assembly line and kept refreshing the paint on their hands after each mark.
I was surprised my 1year old did as well as she did with putting down her hands 4 times! It may have helped that she was working on a Ritz cracker but I still think she did great. These were super easy to make and I've already used my mother's day gift twice!