I'm not a big fan of large saddle bags, Especially those that flop when a horse is at a canter or trot. I prefer more the snug fitting type of cantle bags.
For most afternoon ride, I can easily fit enough stuff into a good secure cantle bag that has water holders on the two ends. You can put a baggy of basic 1st aid supplies, a few matches, a space blanket and several granola bars, jerky or even a can of peaches in the cantle area. Two water bottles on the ends and you are good to go and your horse will be happier with out the floppy bags bouncing on his kidneys.
When Hunting season comes around, I do use the traditional saddle bags. Mainly because I carrying so much more stuff for hunting. Knives, Binoculars, meat bags, extra clothing because of the fall weather, spare ammo for the guns, etc. But I rarely ask the horses for faster speeds during those rides. Because they are already being worked hard because of the extra weight.
When I go camping, I don't pack my camp gear on my riding horse. I'm a big guy and feel that I'm already pushing my horses limits to carry me across the mountains for 8 hours. So I bring along an extra pack horse and load the sleeping bags, tents, food, cooking equipment, spare cloths etc on the pack horse. You can usually get 2-3 peoples gear on 1 pack horse.
The traditional leather saddles bags look great. But I just don't find them as functional as some other choices. And they definitely are not cheap.
Look at the black horse, with the blue cantle bag. I have my lunch inside. Two water bottles and a rain slicker all tied to the back of the cantle. The look at the grey horse with the black corudra saddle bags that flop against the horses flanks.
There is a time and place for each product. You can not buy them all to start with ( unless you are richer than most of us). The cordura Nylon bags are cheaper. Very servicable, easy to clean and low maintenance. They don't offer the look that you probably want in the show ring or parade, But they work great for trail riding.