Another rear rack benefit , particularly if you add dynamo lighting,
is the taillight mount, is on the back of the wheel..
rather than the front of the back wheel, just above the brake.

Most bags seem commuter oriented, O bag is going to keep
your papers, and computer dry. at a cost of $300.

Touring and C and such, sewn, come with a rain cover .. resistant, not "proof"

as a single bag , it is handier to sling it over my shoulder
than a pair of panniers that I have to haul in my hands ..

M bars and Ergon grips is the way I went.., Tour bag..
2nd hand, so some one else chose color

have 2 now, so a companion has a loaner.. to go out, together.
T3 is black , M3L, green.