Fun with Tyvek | I Made It, but I've Got No Idea What It's Good For

In a fit of inspiration I grabbed a Tyvek mailer and flipped it inside out. I also grabbed my Spiderman Lunchbox:

I crammed the lunch box into the bag, flattening the bottom out:

With this bag design, two triangles appear in the base of the bag. I marked them off with pen, and then went over the lines with the sewing machine:

I sliced off the now extraneous triangle and flipped the bag inside out:

I now had myself a neat little sack. The challenge: how to turn this into a functional bag? It needs a closure and perhaps straps.

One attempt I made was to add a barrel hitch into the mix:

While functional, it's too fragile to use in a real-life context.

I'm calling the project incomplete: it's interesting and shows promise, but I'm not sure for what. Any suggestions on where to take this?