I believe that one can up the 6 oz bottle to their 8 oz. It's just a tighter stretch.
Pooh,
I think most everyone who is training through a hot summer and warm fall needs some form of carry hydration. Though, honestly, i am not a fan of fuel belts. They work and work well - most do not bounce and there is little in the way of sloshing. I just find that they get hot quickly and deplete quickly. Most folks who run distance need more than 12 oz of fluid an hour to stay level on hydration. Their biggest application in my mind is the ability to carry your own electrolytic mix in a race.
There are several other styles out there.
Water bottles - There are many waist mounted and hand mounted battle systems out there. Generally these carry 20-28 oz. - some have two bottles doubling the capacity. The largest complaint with the waist mount is the sloshing. A have empty bottle throughs around a pound of water and that can be disconcerting.
Bladder style. Camelback is the obvious brand but there are plenty of backpack style brands. -- Nathan by far was the better through out backpack the last time I reviewed them. These can carry 70 oz of water and many have a pocket for keys, etc. I use and love the Camelback FlashFlow. It is a waist mounted 40 oz system that has worked for a decade. In this system, the sloshing is diminished through a set of secondary cinch straps that you tighten after a drink... keeping the bladder tight and non-sloshing.
Drop a bottle. I have used and still use this as well. Simply, you place a bottle in a location that you will pass and grab a drink as you pass. I use this for sport drink on training runs. I have an ice chest and run a 5 mile loop - as I pass the chaste, I stop and take on a little drink. (the remainder of the loop is taken care of with plain water from a bottle of FlashFlow). One word of caution. I once stashed bottles around my subdivision and found that a dog used my bottle as a target for his 'business'. Hid bottles so that you relatively sure they will not be messed with. I know Frank on this board uses his mail box as a bottle anchor.
Runa park with water fountains. - This works well, but before relying on the park's water, runa hard shorter run to see how well the water tastes while your body is under stress.
Now all systems out there will work and work well. Note that it is a very personal taste and not everything works for everyone. As an example, I need to take in about 25-35 oz of fluid an hour in the middle of the humid summer. A 12 ounce system is not going to work for me. I can see running a marathon with a 4 bottle system in cooler weather where the race is offering a sport drink that I know will not work for me.
One other thing for cooler-longer drinks in a fuel belt or water bottle. Prepare your drink the night before. Fill the fuel bottles about a third to half full and place in the freezer. Only go a quarter full with a regular larger bottle. Then in the morning, fill the remainder of the bottle space with cooled drink. The bottle will stay cool much longer.