Hi,
I have the
large topeak wedge saddle bag and it fits alot in it.
On a long ride i would carry a spare tube, patches, multi tool, tyre leavers, sweets/snack and a lightweight jacket and theres still room for other things, ive fitted key, wallet and a phone in along with this lot. Theres a pocket inside for change etc and it can unzip to folt out a little bit more space.
I got it because there is a strap below it to hold my pump aswell and a loop to clip a light at the back pocket.
Brilliant bag and holds everything you could need, although you may want to go with a smaller one and just use your jersey pockets for some things.