I’ve been really happy with this bag on a western saddle. I can fit my full length Muddy Creek coat in it (rolled) along with snacks and a few small items.
http://www.outfitterssupply.com/TrailMax-500-Series-Cantle-Pocket/productinfo/WTM530/
low profile, roomy, adjustable.
this is a great ‘horn bag’ for holding a small camera, chapstick, snacks, gloves, leatherman, etc. …
http://www.outfitterssupply.com/TrailMax-500-Series-Front-Pocket/productinfo/WTM502/
this stays on my saddle 24/7. Again great for small items, hoofpick, horse treats, stash your gloves and sunglasses.
http://www.outfitterssupply.com/TrailMax-Pommel-Pocket/productinfo/WTM170/
I kinda hate this one. It is annoying if hung from the pommel unless it’s also snugged to a breast collar - it’s going to wallow around some. maybe you could rig it on the D of a rear girth
http://www.outfitterssupply.com/TrailMax-500-Series-Saddle-Water-Pocket-w_Stainless-Steel-Bottle/productinfo/WTM503-SS/
For ‘saddle bags’ I like anything insulated and that closes with velcro. Clip closures and buckles are fine for trips where you won’t get into them from horseback, but are kind of a pill if you do. Don’t use ice- use freezer packs or bottles of frozen water you’ll drink when they thaw. Warning they’ll be noisy while they thaw
For day tripping and packs I don’t have to clean up/air out/worry about- get these:
http://www.outfitterssupply.com/Canvas-Saddlebags/productinfo/WSB300/
we’ll buckle both buckles, but leave the one closest to the rider, looser, so you can get things out more easily from horseback.