I got a lot of questions about these at Anime Boston and a lot of people disappointed that I wasn't making them to sell. But I'm not because I used a wonderful tutorial/pattern from here on DevArt as a jumping point. ^^Shadow Heartless Plush Pattern
I made a few very minor changes to make them work for my purpose:
1. I only wired the antennae. No point in wiring the whole thing, since the belly is meant to be hollow.
2. I extended the zipper line to make a bigger hole.
3. I sewed straps on. The little one is true to the pattern size, so I just sewed one strap between his shoulders (more like a purse). The big one is more like a backpack (it stands about 2 feet tall) and has 2 straps, both extending from the back of the head to behind each leg.
4. To make the big one so big, I added 1 inch around every pattern piece, except the body, which I added two inches around. It's somewhat disproportionate for a Heartless, but then you can fit more stuff in it! My whole group had their cell phone and wallets, plus a small bottle of water in it.
Otherwise I sewed everything together just as instructed. ^__^