Yup, they give out bags at the entrance, at the wristband sites and even at most of the candy distribution areas... there were childrens t&ting and they would ask parents where their bag was and if they didn't have one, they handed them one.
I saw Disney Princess ToT bags at Walmart today for $0.42 if anyone is interested! They are just plastic bags with handles but perfect to toss when finished (if you need to) for that price .
There were also some cute plastic Mickey trick-or-treating pumpkins for sale in stores all over the parks and resorts. If we had room to pack them on the plane, I would have bought some. The treat bags handed out at the park were certainly fine.