backpack for running

If you don't already have one, it may be a spendy route...but I use the camelback pack without the water bladder in it if I want to do something like that. I have the 70 oz one and it works great.

http://www.trisports.com/cb-rogue-70.html

I agree on the Camelbak, I have a couple of camelbak packs, one is the M.U.L.E it's a slightly larger pack but super comfortable and plenty of space, I've done many long runs using this with all the gear I need for being out all day.

the other I just started using is the Ultra LR vest, it has good storage for a long run with pockets and a netted area on the rear that holds lightweight jacket/hat/gloves/tights.

both have good fit systems that will enable you to dial in the pack to avoid bounce etc (just did this myself with the LR vest)

The M.U.L.E can be picked up under $80, the vest is a little more, but for running an errand or for carrying a decent change of clothes I go for the M.U.L.E anyway.

ETA: I prefer the M.U.L.E and Ultra LR as they both have waist straps and I think that helps reduce bounce (for me anyway) the rogue in the first recommendation is a great pack, I looked at that  but went for the LR for the waist strap

I have and really like the Nathan Endurance.  Here is a link.

http://www.nathansports.com/our-products/hydrationnutrition/race-vests/endurance

I'm with everyone else on Camelbaks, either with or without the bladder.

I first tried them on longer trail runs so I could carry water, and hated the sloshing. What I've found is that you need to (a) fill bladder all the way up to the top so there isn't an air pocket and (b) cinch it down well (that's where the waist strap and sternum strap come in), and keep cinching down as you empty the bladder. Liked it since then, it's nice to be able to carry a little extra stuff along with your own supply of water when needed.

I really like the products made by Ultraspire and Ultimate Directions. Both are designed by ultra runners for carrying varying amount of stuff. The packs themselves are lightweight, well-made, and very functional.

Robin