I use a simple camelback mule if I am going somewhere where i may need to bring something to / from, but mainly for locks and lights and such.
bigger runs, like food shopping or delivering stuff, i take my schwalbe messenger bag, as it is fully waterproof and is half of an old tyre, which is badass.
and little jaunts into town i use a Fanatic leg bag as it is just big enough to hold my D-lock, keys, wallet and phone.
I have a normal rucksack, good for carrying groceries and my bike locks, a bag is always good to have, or if I go on a long distance ride I can carry food and drink in it.
i have a nice selection of ermmm 5 ish bags. all backpacks in different shapes and sizes, i have a saddle bag but i never get around to using it, wish i did becouse its quite nice riding with no bag
been thinking about them bum bag/fanny pack things i seen a few riders wearing
i got a handy camel back style bag(cheeper company) i took the water sack out and use it to just hold what i need, the thing is seriusly tiny so it dosnt get in the way when im in the drops at 30+
True! It makes the pack not sit properly on my back. Plus the bite valve keeps leaking.
What I really don't see the point of on mountain bikes are bottle cages! Drinking out of something that is bound to get covered in shit off the trails does not appeal to me. I find it amusing seeing cage mounts on the underside of full sus frames! (mine included)
I've tried a great many bags, and these have time and time again been the absolute best I've used (I'm super impressed with the Lezyne trunk bag at the moment). In addition I have to say that water on the bike is far better than on your back. My touring bike has four water bottle mounts, my XC bike has two, my fixie and winter bikes both have just one. Every time these bikes get used those holders get used. Yes, the bottles get dirty, but I'd rather not wear a backpack if possible. You don't get as sweaty, and the weight is lower. Both bonuses in my book.
I dont usually take a bag, but my multitool lives in my back pocket. If i do take a bag, for a day ride or summat i have the medium sized fox "camelbak" type bag which i like because it has plenty of room and can hold pads or a helmet if it needs to