Sackville SaddleSack XSmall

Perfect for minimal loads and no grocery shopping. Easily holds a cell phone, wallet, keys, tools, gloves, first aid kit (????), and an apple.
Made out of 16oz per square yard fabric from a family-owned mill in Scotland—the same as all Sackville bags.
As a saddlebag, it requires saddlebag loops. All current leather saddles have them, and some plastic ones do, too.

And it wasn't designed as a handlebar bag, but it ends up there a lot because it works well on most bars. The two upper straps grab the bar, and the lower (seat post strap) grabs the stem. If for whatever reason it can't reach the stem (cables or junk in the way?), let 'er dangle, no harm done.

One compartment, easy to stuff.

Cubic inches: 140
Liters: 2.3

Sackville SaddleSack XS
20cm/ 8" long
13cm/ 5" wide
9cm/ 3.5" tall