I realized there was one type of bag missing from the other day’s master post about patterns to learn to do well. That’s the square zippered bag, which looks something like this photograph. It has a square base, it’s somewhere between 5″ and 16″ long (depending on whether you use a 9″ zipper or a 20″ zipper — I don’t recommend a 7″ zipper, the bag isn’t long enough to be useful (though I suppose you could make it a deeper bag and maybe it’d be ok?). No matter — in most sizes, it’s a great tool. 
It’s common for men to use this sort of bag for shaving cream, a comb, and other hygiene equipment when traveling; my family calls this a dopp kit, although where the term originated from, I’ve never been able to find out. It can also make a nice pencil case, as well as being a small arts supplies bag suitable for a simple watercolor set, for example, and maybe some brushes. I forgot to put in the tabs on this bag, but usually there’s a loop along the zipper line at either end, so you can hang the bag from the hook in the bathroom when you’re using it as a toiletries bag, or otherwise hang it out of the way so it doesn’t take up table space. 
My least favorite thing about this particular bag is that you can assemble it the easy way or the hard way. The hard way involves turning, and fiddling with the zipper a lot, so that all the seams are invisible inside the bag. This involves a LOT of measuring and precision cutting, and it’s hard to do well. Here’s a tutorial on that, which is not the way that I made this bag in maroon and orange shown in these photos. The hard way will have all the seams hidden from view, using a turning mouth in the space between one side of the zipper, and the lining fabric. This is a very tricksy way of doing this, and it’s very hard.
I used The Easy Way.
The Easy Way, which I learned from this tutorial (but is also explained in this one) uses zig-zag stitches on seams on the inside of the bag, but not between the shell and the lining. Thus, the bias-seams on the inside create the triangular flaps (seen here in the second photo, inside the bag, at the opposite corner of the bag from the camera), which are sort of untidy.
