Amazon.com : Ibera Bicycle Triangle Frame Bag : Sports & Outdoors

I have this in the large size, and it is big enough to fit a folded change of clothes and several other smaller items. Your needs would probably call for the medium. It's well constructed and has two extra pockets, one on the outside and one zippered on the inside for smaller items. It's easy to install and remove as well.

Amazon.com : Timbuk2 Seat Pack XT : Bike Seat Packs : Sports & Outdoors

However, for how small your items are, you could probably get away with a small saddle bag. I have the one linked above in the medium size, it's enough for a spare tube, tire levers, 2 CO2 cartriges, patch kit, and a few other tiny parts like allen wrench etc. It also has a handy clip on the inside flap for keys.