I made this drawstring stuff sack for my son's blocks. I made it out of a t-shirt and the bag ended up being so big, I would need to buy more blocks to fill it up!
I took a t-shirt and cut it off below the armpits. You will use the hem of the shirt as the drawstring for the bag.
I added some stamped fabric (see the tutorial I made for fabric stamping here). If you want to add stamped fabric patches like I did, add them before doing any assembly of the bag.
To make a square bottom for the bag, I measured the perimeter of the shirt (44") and then cut a rectangle piece of the same perimeter. I cut a piece that was 9" x 13" x 13" x 9".
Then I pinned the rectangle to the unfinished side of the t-shirt. Then I sewed the rectangle to the bottom of the bag.
I opened up a small part of the hem to put the drawstring through and then reinforced it so it wouldn't continue to unravel.
Here is what the bottom of the bag looks like: