I usually wear a backpack, sling bag, or a mess bag. Recently traded a pack for a trunk bag. My back is a lot happier in these warmer temps. The main drawbacks to the trunk is that it partially obscures my seat post mounted light in standard form and completely blocks it if I expand the bag upwards. Also since it is not a QR type, mounting/removing the trunk can become tiresome.
I'd like to give panniers a try again, but heel strike is a major concern. My bike has a CS of 16.3" and the rack has a deck length of only 12". I'd rather not have to invest in another rack if at all possible. I just need something basic (no Ortlieb or Arkel due to budget constraints) that I can rotate the mounting hardware just enough to angle the bag to avoid heel strike.
I would suggest looking at the other end of the bike.
A Porteur rack is big surface, you can tie your back pack down,
and bring home pizzas.
Or get a front pannier rack, typically, for 2 smaller front panniers..
I have 2 Ortlieb Sport packers, on the front, of my BikeFriday Pocket Llama.
Another bike, with 700c wheels, I have one of Paul's, rather adaptable
Aluminum Flat bed Porteur racks.. room for a .4M pizza pan ..