The PDF I thought I could extract pictures out of turned out to be of the wrong US Army publication - no pictures.
But I've found some pictures that aren't on antique auction/sale sites, or blogs, so will probably be available for a bit.
This picture shows a 1917 Officer's equipment, including shows the cantle bags - the big one hanging from the back of the saddle (I've always understood the cantle to be the "backrest" part of the seat, so calling these cantle bags seems to be a slight misnomer, and/or I'm being pedantic. Or I'm wrong. Since my horsey/tack knowledge largely is book-learned, this is vory possible). The picture nicely shows how the cantle bag buckles to the saddle. The flap has a seam (not really visible in the picture) so it wraps around the side of the bag - it isn't just a wide flap that's gotten creased through time/use.
That picture also shows a bag hanging from the pommel (front) of the saddle, plans for which I've also been eyeballing. The pommel pockets are done as a pair, and the connecting bit includes a hole that I was assuming went over a horn. Except I now remember that in this time period the cavalry was using McClellan saddles (link to Wikipedia article), which don't have a horn. Presumably the hole is there to make it easier to tie the pockets to one of the loops on the saddle.
This picture shows an 1896 set of equipment, including the saddlebags I was thinking of adapting as a satchel body, until I found the cantle bag pattern. You can't see it in this picture, but the two saddlebags are permanently sewn to a wide, shaped leather piece that's under the blanket roll.
I know a couple people occasionally have link issues, here's the bare URLs:
1917 Officer's equipment: http://www.militarymemorialmuseum.org/_photos/images/1917-Whitman-Officer's-Sadd.jpg
Wikipedia McClellan Saddle article: http://en.wikipedia.org/wiki/McClellan_saddle
1896 equipment: http://www.militarymemorialmuseum.org/_photos/images/1896-McClellan-Saddle.jpg
April Marches On
14 hours ago